Doomsday

[Killane]

This is an idiot question but I want to make 100% sure I'm right.

all things being equal, after you resolve doomsday you have

5 cards in your library

doomsday in your graveyard

the same hand you had before you cast doomsday

right?

(the crux of this question is that doomsday doesn't get exiled because it hasn't finished resolving yet, and I want to make sure I'm right?)

[Anusien]

Correct. The last thing a spell does while resolving is go to the graveyard, after all its other effects have happened.

[Yare]

Assuming there are at least five cards between your library and graveyard when Doomsday resolves, yes, this is what will happen. Doomsday is still on the stack while it's resolving so it doesn't get swept up into all this exiling. The last part of the resolution of a spell is putting into the graveyard; by that time, Doomsday will be done exiling things, so it just goes to the graveyard.