I feel like assigning healing duty to an NPC that i'm running takes the risk out of the game. The only recourse I have is that there's only one healer, and if you're out of their line of sight or if the healer is otherwise preoccupied you might not get your pre-ordered healing.

How do you handle NPC healing, or healing in general in your campaigns?

All my NPC healers charge for healing, upfront, no deals, and they do not go into dungeons.

well except that one guy, but, well, um, he’s on the pits with his god and so his stuff doesn’t always work. And he’s usually drunk. 

but you can pay him in booze.

I think the necessity for an NPC with healing abilities depends on the party size; a medium-sized party (4-6) may not need one, as I'm sure at least one of those characters will have some form of healing. Keep in mind that in 5th Edition defeating enemies is far more effective than attempting to out-heal the damage, so having a designated 'heal bot' is not going to be all that effective. Prevention is better than the cure, and all that.

Healers may exist in your world, but few of them will have the readiness to enter a dungeon and risk their life. Some will want a share of the loot, others favours, and some cannot be tempted by any means short of magical influence. And even if they do go with the party, they might not stay: roll for morale every now and again and see if they flee, or do a bit more than heal. If the party neglects them, the healer might feel entitled to more loot or will let people know not to trust them.

Rather than a healing NPC, you can throw in healing potions as loot or have merchants sell them. Sometimes there'll be a well, fountain or other vessel for liquid that looks like it would do anything but heal someone, but sometimes fortune favours the bold. And if the players pay their respects to statues or shrines, they might have Aid and other such spells cast upon them in thanks.

Finally, it's then up to the players to not die. If they have no means of healing themselves they should try to avoid unnecessary combat, and retreat when it's going sour.

Quote from Abbraxxus >>

How do you handle NPC healing, or healing in general in your campaigns?

 I don't. That's the Players' challenge to overcome. 

They choose their PC, their abilities, and their roles in the party. If they don't have the money to afford a retinue of followers, or the social skills to gain a sidekick they can always do what us paltry humans do.... apply real-time risk assessment and mitigation strategies to prevent us from being injured.

I rarely have NPCs tag along with the party, and when I do they are generally martial characters or arcane experts. Once or twice, when I've known I was throwing my players into something exceptionally deadly, I had a cleric travel with them to provide buffing spells and stay on Revivify duty. He required the party to provide him with diamonds up front and kept any leftover healing components when the journey was complete.

Usually, my players figure out healing for themselves. My current party doesn't have a dedicated healer, but they're tied to a guild, so I expect they'll requisition healing potions and medical kits when they come back from missions.

One benefit to an NPC healer is that you can kill them off without scruple. The party gets into a nasty fight, an they come out barely alive and needing to fight their way out of the hive of the blood-bug they just killed, only to find the Healer is dead! Problems to solve, players!

But I agree with the sentiment that the party needs to solve their problems themselves. If they have no healing, despite there being many routes to getting it (feats, potions, kits, levels, spells, items....) then it's on them that they can't heal. Giving a party committed 100% to damage output a free healer makes them decide to never play a healer, because why invest levels into it if the DM will give it to you for free?

Quote from Kaavel >>

Quote from Abbraxxus >>

How do you handle NPC healing, or healing in general in your campaigns?

 I don't. That's the Players' challenge to overcome. 

They choose their PC, their abilities, and their roles in the party. If they don't have the money to afford a retinue of followers, or the social skills to gain a sidekick they can always do what us paltry humans do.... apply real-time risk assessment and mitigation strategies to prevent us from being injured.

 
This👆It’s not the DM’s job to solve the problems, that’s the players’ jobs. The DM’s job is to present the party problems to solve.

If the lack of an Npc healer affects a smaller group (i.e. less than four players) detrimentally then it becomes my job as a dm to fix the problem.  I have no problem running an npc cleric.  I am not going to punish a small group by making them pay for cures. Recently one of my groups that has three people and they made sure after a divvying up treasure this last session they gave the NPC Cleric A full share of the treasure plus paid the gold to enchant her armor and weapon.  To be very clear i did not even hint she needed anything they just went ahead and did it.

It was a weird moment for me.

Quote from Xeresia >>

If the lack of an Npc healer affects a smaller group (i.e. less than four players) detrimentally then it becomes my job as a dm to fix the problem.

 Ensure that there are plenty of healing potions to be found. Build encounters that aren't likely to render a PC unconscious very quickly. Allow plenty of options for short rests (so that they can use their own hit dice to heal).

All much easier than managing an DMPC/NPC in the party.

Quote from Xeresia>>

If the lack of an Npc healer affects a smaller group (i.e. less than four players) detrimentally then it becomes my job as a dm to fix the problem. 

I am not going to punish a small group by making them pay for cures.

 Assigning intent to life consequences, or in this case in-game consequences, doesn't make this less viable an option. This isn't a punishment, unless you make it one. No one is suggesting that anyone learn any life lessons here, if there are some nuggets gained through trial and error, fine. If you feel like your are punishing your players for a choice they made, that truth lies in the mirror.

Quote from Farling >>

Quote from Xeresia >>

If the lack of an Npc healer affects a smaller group (i.e. less than four players) detrimentally then it becomes my job as a dm to fix the problem.

 Ensure that there are plenty of healing potions to be found. Build encounters that aren't likely to render a PC unconscious very quickly. Allow plenty of options for short rests (so that they can use their own hit dice to heal).

All much easier than managing an DMPC/NPC in the party.

I will not ensure they have plenty of potions, healing or otherwise Resource management is a player issue. Easy encounters do not challenge the party! I build encounters to challenge the party, death and unconsciousness are sometimes biproducts of that, but they are not the goal,  The rule at our table is two shorts rest per long rest at max however, those short rests are subject to random encounter rolls. the npc cleric takes no extra brainpower for me to run and it makes my small group happy and does not break the game