Units without daily resources

I'm sure this has been asked before, please point me to the appropriate thread, or just explain it to me briefly, please.

When land units no longer have sufficient daily resources (as in the case that virtually all - but not all - of their provinces have been captured, and assuming they don't have resources stockpiled or being fed to them daily by a friend), what happens?...

Do the units blink out of existence at day-change? Or do they slowly fade in strength and evaporate every day?

Thank you.