So, I have been thinking a lot about what angels do in Forgotten realms if their deity is killed. Do they lose their power, or do they still have it and they are just not bound to a master? Will another deity claim them as their own?

That's honestly an interesting question! Subscribing to the thread in case anyone answers :)

I don't really know but perhaps you could base it on what happened to Hoar?

"With Tyr's death, Bane recruited Hoar as an exarch, causing Hoar to take on a more evil persona." - from the fandom page on Hoar

I don't think they would lose their power. Maybe they drift along and might eventually side with another deity that was similar to their old god? I don't know what the actual WotC approved version is but this sounds plausible.

Quote from Wes_B >>

That's honestly an interesting question! Subscribing to the thread in case anyone answers :)

 Also, you can subscribe by clicking the tools button in the top right corner next to reply and search. It will have a dropdown menu and one of the options is to subscribe. You don't have to add a post to subscribe, you can just do that.

Yep! I know :)

Okay. So let's say you're an angel... or a solar, planetar, whatchamacallits, whatever... and your deity dies.

Well, the way I see it you've got three options: Move up, move out, or move on. 

Move up: You've been working for that deity for f*cking ever! And you've always done what needed to be done, and heck you've gone above and beyond more times than you can count (and you've got an Int of 25). And sure, this is what you were made for, and this is what you've dedicated your entire existence to, and maybe this is just the way the universe is supposed to unravel, but you know what?! You've always felt held back. You've always felt like a CR21 doing a CR16's job. Maybe the big guy was keeping you on the slow track for a reason. Ever think of that? Maybe he didn't want the competition. Well bud, this is your chance! The big guy is gone, everything's a mess, everybody's looking for someone to turn to... and there you are. You were never gonna be handed the Brass Ring, but this is your chance to just f*cking TAKE IT! Be the boss! Accept the adulation of his wayward followers and let that power fuel your rise. And sure, maybe you're not an actual "official" deity... yet. But like those silly little mortals sometimes say, "Fake it til you make it."

Move out: You're not a deity, but comparatively speaking, you're damn close! You've seen a hundred generations of elves come and go. You've got the strength, the wits, and most importantly - the charisma to do whatever the heck you want. Sure, you were happy to dedicate all those nearly-infinite capabilities in the service of your former boss... "were"... but he's gone now. Come Monday morning there's no clock to punch, no cubicle awaiting, no inbox of paperwork. Nothing. You're free. You can finally do all those things you've dreamed of doing, but the job was always in the way. Sure, you may not be as powerful as when the boss was in the chair, but you're still a handful. And now that you finally have a chance to stop and look around, you're beginning to realize that these worlds have a heckuva lot more to offer than endless millennia of service and duty. So get out there, big fella! Have some fun! Stretch those wings for a change and let the winds take you where they will. 

Move on: Who are you kidding? You can't just walk away from your duty! You can't just turn your back on all those eons of faithful service. This is who you are! This is what you were made for! If you had really wanted to go off and slake your wanderlust you would have done it by now. But you're still here - the servant of the faithful -the guardian of the defenseless - the light in the dark that fills hearts with hope. Your boss may be gone, but you're still here. And the job still needs to get done. Do it. And trust that in time you will find another deity who inspires you to service. You will find another flock that needs your protection. You will find another dark land that needs a beacon lit. For while the bosses come and go, you will always be there, faithfully serving the cause. You will persevere. THAT is what gives the people hope. Be that example for them. 

I'm sure there is an office somewhere in the cosmos dedicated entirely to this subject.  That place where all the angelic forms have to go signed in triplicate to get validation.  They assigned you this gig 3 worlds ago, and if you played your cards right, you'll enjoy the one they assigned you to this time too.  I mean, it's not like they are only dealing with Toril... there are scads of dedicated planets needing celestial messengers and dignitaries.  You just hope you didn't put the wrong form in to the wrong bureaucrat in that office or it may be a long time serving a small time deity in a frozen wasteland with 50 followers.  

Just wondering, since I'm not deeply versed in FR lore.  Are Angels a notable presence in FR?  Anyway, outside of setting specific cosmologies, MM says Angels are formed from a gods astral essence.  One thought would be that angels are merely extensions of gods, albeit with a measure of autonomy, so maybe if the god is killed the angels ceases to exist as there's no longer a connection.  Perhaps as a benevolent act another good god could salvage those disconnected essences (to either expand their own power or as a "shard" to possibly restore the fallen god), or an evil god or godslayer can lay claim to them and ... turn them into something else.   

IRL theologies that take angels seriously as well as fictional treatments of angels, some argue angels lack the autonomy and agencies humans have and so the extension/agent process I've proposed above could fit.  

Of course the MM offers Fallen Angels too which are disconnected from their god, so a "break" can be done.  Rather than Angels fallen to Hell, you could postulate sort of "Ronin" angels who can deliver their gods legacy to other gods with overlapping portfolios.  As a counter to the MM though, there is lore (I'm thinking particularly of the end of Legion, the novel sequel to the Novel version of The Exorcist) that postulates a "fallen" angel may lose their way as an agent of their god, but the connection between their god and the fallen is still there (so even if you go full on Devil as an angel, you're still acting within your god's domain ... and thing get sort of heady in cosmic view of morality way from there  ... so if you want an angel's existence entirely predicated on their god's existence and essence, there's that.  

The closest we have to that is Zariel... an angel that rules the First Plane of Hell... I think that's how that plays out... I avoided reading a lot of the adventure module because we were going to be playing it and haven't made it that far yet.  And all in all, this is the playground of the Dungeon Master.  Any and all of this can work (and many more things beside), but it's up to the DM to put the strings in place and play them to make the world work they way they want to.  Ours is very averse to anything resembling heaven or hell and religion, so I'm sure what we encounter in the planes of Hell will be different than what I read when we finish dealing with the parts of the module he lets come through.  I expect we'll see a lot of punishment aspects, but I doubt we'll get some connected cosmology.  

If I were dealing with overtones of angels and demons and devils, I would have a lot more messengers and a lot of dream sequences to my players.  I see the angels as very good ways of delivering messages and hidden meanings from more powerful beings... and have no problem allowing the players to summon their own potential infernal influences with messages of their own.  

Zariel's background is definitely expanded upon in DitA; but the gist of it appears elsewhere in 5e, Volo's and Mord's I think.  I don't want to spoil your adventure.

They should not lose the power they have, instead there should be like a 1d100 year claim period, during which the angel may be claimed by another deity. If time runs out they should become a fallen angel, as they can no longer be known as a celestial without a deity. If your players kill the deity the angel served then it should never become a fallen angel instantly, as it will be technically serving the deity in one final act, so an angel of revenge should not lose any form of power and can not be claimed by a 2nd deity until it gets revenge for its master.

sorry for the long reply... hope this helps!  

I'd say that their divine power is severely reduced - perhaps becoming an Aasimar. Maybe they cease to exist at all, or go insane?

Like any good vassal, they find a new lord to serve.

Depends on your setting, if there is a pantheon, then maybe serve another deity. Other options would be becoming sort of fallen, declaring themselves as the the new deity like a lesser god...

I have a character in my homebrew world who's somewhat similar. He's a fallen angel who made pacts with beings of darkness, but he also retained his angelic powers, except that they became dark powers instead of light ones. I would rule that an angel who's deity died would still have their powers, but would be lost and without purpose.

Quote from Thauraeln_The_Bold >>

I have a character in my homebrew world who's somewhat similar. He's a fallen angel who made pacts with beings of darkness, but he also retained his angelic powers, except that they became dark powers instead of light ones. I would rule that an angel who's deity died would still have their powers, but would be lost and without purpose.

Except he's apparently undead.

Quote from Halfastbracegirdle >>

Quote from Thauraeln_The_Bold >>

I have a character in my homebrew world who's somewhat similar. He's a fallen angel who made pacts with beings of darkness, but he also retained his angelic powers, except that they became dark powers instead of light ones. I would rule that an angel who's deity died would still have their powers, but would be lost and without purpose.

Except he's apparently undead.

 Yes, but that's irrelevant to this discussion because he wasn't undead for quite some time.