yes twin emperors for me too :/
6527 wipe on 25 Sarth 3D
When my guild first started attempting 10 heroic morchok, we actually killed the twin just as he stomped which wiped us. The other group died with 3k left on the 'better half' lol. When we regrouped, it was insulting to see the dead twin next to a new boss hehe
wiping on naxx 25 in 3.0 grobulus on 9k hp left and i was lst 1 alive
They can also die the other way round too, I'm not sure what would have happened if we'd have died on our side with Morchok dead... We got the guild raid challenge thing popping up as completed, so I assume it stays dead. :/
The second time we did it, we killed Morchok first (last time they killed Kohcrom and then had morchok go deliver justice as our morchok group wiped) and the other group had 2% or 1% left on Kohcrom and were still fightning him well after the new healer got his achievement.
It's really only based on Morchok
HP sharing is not instant, they update once in a while, we have it all the time.