NPCs survival needs

NPC characters that do one thing are as good as a cardboard cut outs.

The interaction with NPC characters should make the player feel like that the NPC is not just there to act as a terminal or as a gun.

NPCs with survival needs generate behaviours that will make them more believable. Skyrim gave many of the characters in towns a place to live and work, they would respond to threats and return to their routines when normality was re-established. This added to the 'special sauce' the game had which contributed to it's success.

NPC characters using recharging points, seeking medical attention, resupplying O2/H2, alms or arms create journeys and activities not directly interacting with the player but observable by the player.

NPC character combat.

NPC characters that know no fear, are irrational, NPCs with no courage offer no challenge or support. This could be a numbers calculation, with a desperation and group loyalty factor based on the local zone of battle. Simple strategies like hold position, retreat and advance on the target would be good to see. Advance strategies would be reinforce position, escape with covering fire, flank target and so on.

Diplomacy - de-escalation. (Is this possible, would it offer gameplay value ?)

For some this post is offering gameplay that is not SE in their minds, I would say give it a chance, it will not necessarily crash you PCU ambitions, you may end up liking the additional depth.