I've been running a semi-regular game for some of my friends for the last 6-8 months now. We started out with a homebrew story that had a lot of political elements going on. It was going well until certain real world events burned us out on politics. So instead of completely scrapping everything I decided we'd just switch gears and I started running Curse of Strahd. It's given us a nice break. 

I wont go into what's going on in CoS, but they've made headway and are doing pretty well at gathering information, making decisions, and preparing for things... so they may "succeed" and survive at this rate. And if that's the case, I'll need to drop them back in to the world they came from. I know the Mist could take them anywhere I want, but they are going home. Because I'm the DM, and that's what I am preparing.

My idea is that the Mist returns them to their home Prime world, but a few years later. The story they were working on has been completed, but by other adventurers. There has been a brief peace. But now things aren't quite right in a few of the surrounding villages. Children have gone missing, yet returned unharmed with no memory of events, months later. This is going to be my first hook into an underdark campaign. Something in the world below is stealing human children.

I'll continue to update this as I come up with ideas and flesh more of it out.

I'm running Curse of Strahd with my kids.  My daughter is stringing along the Baron of Valaki and his family, making them think she is an ally and might marry the son, creepy Victor.

My players are in Valaki as well. Rictavio is on the verge of revealing himself to the party, but isn't quite sure they are trustworthy. 

I think a time jump makes perfect sense. It seems totally plausible that the rate of time passage could be different in a demi-plane.  All I can say about the setup for there return is that I hope those kids are really changelings! Sounds pretty intriguing all in all.

I'd thought about the children being replaced by doppelgängers, a modified Simulacrum spell, or be dominated by Mindflayers. Each of those is uniquely evil in its own way.

I'm also toying with the idea that the Illithid have Githyanki/Githzerai as dominated thralls. Maybe the party helps set off the Gith rebellion and they have the Queen herself as an ally pre-lichdom. Tons of ideas going through my head.

I've got plenty of time to flesh out and fine tune as they are nowhere near ready to take on Strahd at this point.

I've begun the overland map for the next campaign in Hexographer (old version, not the new one). Started with the Barony the players started off in and just filling in the immediate surrounding Baronies, and the central Citadel of the Kingdom. I have room to expand if I need to, but probably won't. Going too big gets unwieldy and I want to keep it simple. Also added a few "random" feature locations so I can introduce new elements or start from scratch in case things go south Below.

Next up, Mapping the Underdark... This will take more time.