This is what i think may have happened
Bolvar at wrathgate unharmed
Bolvar gets killed by the plague
Bolvar gets incinerated by the red dragons flame but it also brings him partially back to life
scourge come out after the burning to see if theirs anything to salvage
scourge see bolvar is alive and they drag him into icecrown citadel.
The dragon queen sees them taking bolvar jsut before the door shuts
The dragon queen lands and gives you a quest
you go on your merry way while cursing the forsaken