Now my spec ... what if there is a cure to the werewolf bite? (Well, okay, yeah, there has to be). Petrova blood. Since the Petrova doppelganger is so tied into the sun-and-moon curse doesn't make sense that a Petrova's blood could heal the werewolf bite? I think it makes as much sense as anything else having to do with the curse. So, Elena could give Damon her blood and that would cure him.
Jen, we all know you just want Elena to give Damon her blood, stop grasping for straws.