I don't think either. I recon he will come back as him just darker. Ruby said that it can take a while for someoneto become a demon. I recon Dean is strong willed enoguh to hold on and stay humman, maybe a bit darker, but human.
Still wondering how they are gonna get him back into his body as Jensen is still gonna be playing Dean as far as we know!

^^ yeh exactly he CAN'T come back as a demon because the whole point is your humanity (and your body) is burned away and when the demons escape hell and go back to earth (don't know what they look like in hell) they all look like back smoke UNTIL they posses SOMEONE ELSES body!

Well....i think Sam or Bobby(or someone else) will get him out of hell ...but not as a demon but human...if that's possible =[

He will come back but not as demon pissed off maybe darker but not a demon

Neither :P

I think this one would have been the most likely though. And he did become a demon temporarily, eventually.