What happens to the PS3 when you take The HD out?

May be...

I know it don't work With the HD out. But if it was out what would the PS3 do you that it was not in the PS3?

Nope it wont work, you need HDD it contains some Software on it so you wont be able do anything without the HDD.

It'll work; you just won't be able to play downloaded content or savegames.