I don't know man, how many times has Ner'zhul died and come back now? I mean he died at Kil'jaeden's hand, and came back as the Lich King. Died at Arthas' hand, but we find him again again in the Shadowlands. An alternate version of him crops up as a key player in WoD in the interim. At this point, Ner'zhul may well be the cockroach of WoW and just reappears whenever and wherever he wants.