Board Thread:General Discussion/@comment-7453433-20130415113149/@comment-7953253-20130415133322

I'm pretty sure Farkas is permanently essential even after completing the Companions questline, but not Aela and Vilkas. Because if all three of them were dead, what would happen to the miscellaneous quest 'Talk to the Companion leaders for work'? The essential status is there so you don't encounter quest breaking glitches... in most cases.