Hey few more thoughts
1. Have you consider consumable being dropable (simple things, one time character buff before delve or +cond - stress - fatigue one time. Could add huge clutch element when you need that 1 character. It could also be in quartermaster item pool or even be yet another building (alchemist) which generate a potion every week. (Give the player more choice/decision and more control a little to influence certain outcome) Also one way to prep for these difficult delves where you need to go all in
2. Honestly most likely a very low priority backlog idea but what if retirer adventurer could become amazing staff when they are EOL. Could encourage keeping someone till the very end or grooming a star into longer term benefit.
3. I know this was already mentionned and I might be wrong and its alreadt possible but if a hero get poached, It be great that you can get them back or even set tracker on hero so you always know where they are/can get back in contact with them whenever they are up for renewal or to poach them back
4. Bigger Group/Raid type elements. Risk/Reward. It be quite cool to have bigger dungeon where you need to field 5++ hero but where reward/gear is much higher. Also would recommend to make them spammable liek delve so they arent redundant. maybe a random pool of raid that can be done 1/season or something.
5. You could also have bounties for some boss/characters type things
Note: I havent finished the game so some features I recommended may already exist and I dont even know
By the way the wiki (https://dungeonsanddynasties.com/) is 9.5/10. Its litterally open at all time on my other screen, Amazing ressource. One thing I cannot find is anything speaking about quest.