Everything will die to all but the truly bad. The hardest boss will probably be the roster boss. Followed shortly after by the loot QQ dragon.
We know from previous experience that casual guilds struggle with ... Now anyone wanting to raid in tbc will likely continue the grind to filling out their ... re-released so far people thought were going to be so difficult and guild
i was doing speed runs in kara in a casual guild back in BC. And we were all mouse clickers. If those same folks got back together after all this time, we'd crush it even more so.
I ran 2 alt runs in addition to my mainrun in TBC, and there was several guilds doing the same aswell.
With the more serious alt group, we were even realm second group to clear ZA in our karazhan gear.
That being said, to OP most raiding guilds (70-80% on server) failed at transitioning from T4 to T5.
Unless they undertune some fights severly like in classic (mag, gruul, prince, nightbane) I can see this history repeat itself.