How does Cas figure into the boys' Alpha mission?

How does Cas figure into the boys' Alpha mission?

So we all know by now that Crowley is holding Sam's soul, and is making the boys round up the Alphas to help him in his quest to find Purgatory. And Sera Gamble told TV Guide, the brothers will go to great lengths to free themselves from Crowley's control:

"The brothers are tired of Crowley calling the shots, so [in the episodes airing December 3 and 10], each of them goes pretty far to try to solve Sam's problem."

Look for the return of Cas and Balthazar, as well as Winchester-hating demon Meg. Speaking of Cas, Misha Collins told TV Squad that Cas's mission to restore order in Heaven could interfere with the boys' Alpha mission:

"Cas is on his own specific mission, which is to restore order to heaven, and at times it's going to run counter to Sam and Dean's missions. Why are these monsters so active, what brings them about, and why is there so much monster activity? The answer ultimately does lie with something that Cas has something to do with. I can't tell you what that is, but Cas is definitely involved, and heaven and hell are involved."

Will Cas try to stop Crowley from finding Purgatory--or does the angel want Purgatory for himself? Is this all leading up to an epic battle between the leader in Heaven and the commander of Hell? We'll have to watch and see.