I will keep this short and sweet.
The “no NPC needs” mod prevents NPCs from needing food and water (If you are not using this mod you can leave now)
However, the mod does not stop nutrition from being an issue.
At -100 nutrition (or “health” as the wiki calls it) healing while sleeping is completely negated.
In short, NPCs hit -100 nutrition then stop healing.
Solution: Just give the NPC a multi-vitamin before resting.
I do not know if this is a bug, an oversight, or an intended feature of the mod “no NPC needs.”
Sounds like an oversight.
Health and nutrition are different things.
NPC health may drop as a result of radiation or bad food. Radiation hits it really hard.
With no food and no outside factors, health will not drop.
Luckily for them, my 5 NPCs get granola, meat, scrambled eggs, clean water and a bed regularly. Sometime on said bed lies a playboy mag for their leisure also 
I happen to know that PK Rebalancing changes your health value outside of diet. Is it possible to accrue -100 health with NPC’s in that situation and get a total heal standstill? Because it sounds possible.