After the second battle in The Machine, I went in and attempted the final battle with Kane. While the instance quest remained, upon fleeing, the non-instance quest Final Countdown had changed to say Talk to Avery, and upon doing so, it completed as if I had completed the instance quest despite leaving the dungeon without defeating Kane. The end cutscene played as if Kane had been destroyed.

Note that this glitch I cannot replicate since the final quest has already been turned in as a result.