There are many kinds of characters they could have us interact with in deep dungeons, and it's a bit of a shame that right now it's all mobs. Some you avoid, some you approach with different strategies, but they're all just mobs.
But, how about encountering non-combat NPCs in deep dungeons?


Some could be friendly and sell you things, briefly join you, bestow a boon, etc. (Or be evil in disguise and inflict you with pox or a debuff).


Some should be avoided or they will (Legend of Zelda Wallmaster style) drag the party back a floor (or two?) in your current set of 10.


Some could block a path to a side area (not containing the exit) unless you do something. Like:
-- exchange a specific pomander
-- give up some of your aetherpool levels (I like this one)
-- complete a simple challenge or a riddle
-- kill enough monsters to unlock the exit. Someone is guarding it and they'll let you through when "it's safe" (or whatever) and now you have a potential decision to save time and take the exit out, or check out this previously blocked off area with nice stuff inside.
-- could be blocked by a cave in (for example) and if you can find a bomb elsewhere on that floor and bring it you can clear the way (or you could have a locked door needing a key, a Demon wall missing their Demon brick buddy, etc.)
-- etc


Maybe you could find a fairy (or whatever) being harassed by a group of strong (for the area) monsters. If you can clear the pack the NPC unlocks the way forward, or maybe even teleports you a floor (or two?) ahead.


How about an NPC that is there to fight the boss, but you encounter them on, like, floor 55 and if you can escort them through they can help weaken the boss.
Maybe they fight other enemies along the way (potentially complicating things, getting into combat you were trying to avoid, and making you question wether you can save them or should ditch them), or maybe they don't partake in combat, or maybe the monsters know this NPC is here, and they're looking for them, so there are more wandering mobs/patrols than normal so keeping them with you is dangerous now but pays off later.


Etc.
Just some NPCs you can find that shake things up a bit.