They don't get a turn if all of their units are asleep. Similary, on Bolo for example, take out everything but the Beserkers first in the two barbarian boss fights. The Beserkers are on auto and the boss will never be able to cast! (Obviously, the all droid army presents a different challenge and a different strategy is required.)
If anyone is having a particular problem with a boss then i'd be more than happy to write a guide but usually their armies have different troops every game so it's hard to write a generic one....
EDIT: Elwin check here
http://forum.1cpublishing.eu/showthread.php?t=11214