Any time a baddie leaves the mat for any reason, it comes back at full hp and without any effects.
Undead come back at 2hp and double their attack. Any effects are still removed as per the standard rule.
Yes and to add a little:
1 Point and 5 Point Baddies go on the last place if the Initiative, 10 point Baddies, Gearlocs and Tyrants on the First Place.