Yup, Desmond was def on the plane in the flash sideways. The character is clearly important to the narrative, and not just because of the oops-I-didn't-push-the-button plane crash thingie, and the earth-shattering kaboom (TM) that blew the hatch. I don't think he's a "Candidate," but they kind of have to address the whole time travel thing. I'm hoping he'll get an ep that focuses on him, similar to The Constant, and if they do that, they may bring Faraday in at that point -- well, unless he was never conceived in the flash sideways . . .
Anyway, I'm looking forward to next week, when we'll discover that Richard has been Batmanuel this whole time.