Resources in MGS 5 shared between offline and online mode and most of resources are stored online. However offline funds spent first and dip into negative values.
Andswer on How does Mother Base staff morale work? states that negative GMP values hurt morale.
Will morale decrease when offline resources negative but shared GMP value positive?
The online resources can be viewed as a sort of "savings fund".
It seems that you are given a set amount that you can keep offline at a time and once this set amount drops to zero it will transfer more to you the next time you connect to the servers or hit checkpoints in or between missions.
So when your offline resources drop and there is no more online resources to feed in, that is when the staff moral will drop.
If your offline resources are negative but your online positive, some online resources should get transferred over.
If the servers need maintenance before you can get resources transferred you're boned unless you sell some stuff at mother base or whatever.
