
I'm pretty sure that critters eventually respawn.
It is possible that certain evens reset the timers, though, so you might very well find yourself never seeing that occasion during the current content.
That aside, have you noticed your character never sleeps unless told to?

As far as I'm concerned, the whole current story could very well unfold within a few days, though I'd prefer it to be a bit longer.
As for the lockers;
Let's say it wasn't an ancient locker behind an autoturret that hasn't been properly configured in at the very least decades.
You move to an area where you can still see the decomposing remnants of former inhabitants rotting on the floor.
You find a footlocker, it's lock has been picked, and you don't have the key.
I don't know about you, but I wouldn't stash my stuff there.
All that aside, the game currently has a slight problem in that everyone who even slightly worries about his finances (or can craft) amasses a serious amount of charons in short order.
If you simulate, or at least act like you do, a propder underground living with people moving and what not, the players actions would put a strain on the Underrail economy, and I'd certainly expect you to be robbed or mugged occasionally for all that currency the carry around.
And what about SGS, how do they earn their own money?
Shouldn't you pay taxes?
... Thinking about it, chance encounters with bandits aren't a bad idea.