Sam was going to die because it was part of a trial and the trials were killing him. A man of letters had cured a demon in the past and was okay. (he was killed soon after, but curing a demon had no effect on your health). In theory Sam could pull that same exact stunt with Dean and he should be healed in a few days.…

Personally I think one solution (not one i'd like) to the Deanmon situation would be to cure him with some human blood. Sam was one dosage away from curing Crowley himself of being a demon. It shouldn't be that hard to shoot dean up with some human blood.