Per rulebook, page 321 (pdf page 329):
"If the LD test is successful it will reanimate for one last Turn before it returns to the obvlivion awaiting it"
So, the way I read that is that if he makes the LD test at the beginning of the turn, you have one more turn to use him as you wish, then he goes poof. You may use him at any time just like any other model, he does not have to activate immediately, and he is essentially at zero wounds, so wounding him again won't help much, seeing as how he's already dead....again.
SP