Swift Flight Form Quest Missing Whistle

The whistle I need to summon the bird to get the next step of the quest has disappeared from my inventory.

Killed the Falcon, summoned the bird with the whistle, turned in the quest. Before I could accept the next quest, the Falcon respawned and I fought it again. After I killed it, I got jumped by a warlock. By the time I got back to my body, the quest bird was gone and the whistle was no longer in my inventory. So - I can't get the next quest because I don't have the whistle, and I can't get a new whistle because I'm not on the quest.