So i was doing Kael'thas on heroic mode and as he threw us up in the air for Gravity lapse we managed to kill him.
And new in 2.42 is his new death animation, where he says some stuff before actually dying.
Somehow the gravity lapse debuff never disappeared and as he went into his new death animation, we could simply fly around inside the instance for the duration of the buff.
Not sure if its reproducible or not but there it is, it was great fun while it lasted as you could fly straight out of the instance.