What happens to GameObjects in a List when Destroy()'d elsewhere?

I want to have a List of currently spawned enemies, and when one gets destroyed, spawn one to replace it after a delay.

If I Destroy() the enemy when it's hit, would it disappear from or turn to null within that List or would I have to set a flag and later remove and destroy the enemy from the list manager?

Or could I use a 'dial home' message that alerts the list manager when one is blown up?

It'll go null (in that weird way unity objects do due to operator overloading)

You should be able to go through and check for items that are == null