It felt like it could have been a test to me, too, but a test of what? Alternately, I think it was probably a trick: he needed Jimmy to invite him back in. It's possible that angels, unlike demons, need permission. (We didn't see Castiel ask Claire, but I bet if he had whispered in her ear, "Do you want to save your family?" the response would have been a firm yes.)

I am going with the Jimmy did actaully get to go to heaven and Cas is now the only one residing there. Though, that's just me. :)

That's a theory that could work, although it doesn't make me less sad, just sad in a different way. Ow, show. OW.