I thought it was a little peckish of the healer to just bail, especially w/out telling us. Again, to be fair to the shammy, we did occasionally hang back to watch him die yet he survived every pull -- granted, we usually would jump in eventually out of boredom, but he was quite good. But he was just a 45, it wasnt a run thru and I'd have happily traded his dps for the healer, and probably wudda whispered the healer to get him back in if I were leader or had the relationship with him.
The healer was a little thin-skinned, but just a little. It was really persistent abuse for abt 3 mins after the wipe. A 47 priest can find a ZF pug in 5 minutes, why sit in one where someone's calling him an asshat and noob?
I do think, to a certain extent, that they were both wrong. The shaman shouldn't have been rude, and the healer most certainly should have said something before disappearing. Maybe if some conversation had occurred, things would have run smoothly.
That said, it sounds like the shaman thought it was his group (tanking, yelling at the healer, ordering the leader to find a healer right away, etc.), and it sounds like the leader was letting him get away with it.
I'm not sure how long I'd stay in a situation like that, assuming that the shaman was being a jerk about it, as it sounds here. Thick skin or not, I don't generally enjoy being yelled at or ordered about in that kind of manner, and if the leader isn't going to be firm, what happens if there's a loot argument or other volatile situation?
I'm not saying the shaman should have been kicked, necessarily, but some control (warnings, etc.) from the leader would have been appropriate.
Healers tend to get abuse from mouthy people, sadly. I know I had it and very rarely deserved it. Your healer certainly didn't deserve it - lag is a real problem for us because every second counts. A small lag spike can often mean the difference between life and death. Same thing goes for CC - if you miss a sheep, people can die. Pure dps, like the shammy, don't really matter - if they weren't there, the fight would just take longer.
The shaman should have been warned after the first pull where he drew aggro from the tank. That's where the law should have been laid down. Just because you survived doesn't make it alright for him to keep doing it.
Then after the healer leaves, the group leader tries to do gahz'rilla short of one man? That's plain madness. I'd have left at this point.