Forum Discussion
I don't think that DN is supposed to "get any life back" when he uses annihilate. The ability reads that Nihilus "gains max health equal to the target's max health". He does not, however, heal himself in any way.
For example, if Nihilus has 1 health and a 30,000 max health pool, and he annihilates a target with 30,000 health, then Nihilus will have a maximum health pool of 60,000, but still only 1 health.
There are separate reports of Nihilus not gaining health when he has a health steal effect (or under his own leadership, which provides health steal), and when he uses annihilate in a raid for 99999 damage. In that case, his annihilate is doing damage, and you would think that he should thus heal himself a portion of the damage due to health steal. However, the 99999 damage is "white" on the screen, and thus treated as "bonus damage" in the same way that expose is ... you will also find that Nihilus does not heal himself when he has life steal for the bonus damage that he does when he procs and expose.
In both cases, as far as I know, everything is working as intended.