I am handwaving Dean's non-gibbering in insanity as Castiel healing his soul/mind as well as his body when he pulled him out of hell, enough so that the memories are there but muted enough not to making him completely incapable of functioning, since the angels need him to do a job.

But yeah, I am worried that they are making Dean way too broken to come back from this. I hope they are not going with the self-sacrifice for atonement route, and instead having to save Sam somehow will make Dean realize that he has to forgive himself.