Kharn standing back up after being killed by a precision attack.

Had this experience in a game recently and we couldn't find an answer during the game.

Kharn was killed via epic challenge while I still had 5+ Berzerkers in the unit. Kharn got back up like the badass he is, but the ability doesn't say he can attach back to the bodyguard unit, just that he must be set up as close as possible to where he went down.

Is there an FAQ or a written rule about units standing back up and reattaching to their original unit? I can't find anything meaningful.