Here via spn_heavymeta.

I think it comes down to something much more basic. Possessed!Sammy could've killed Dean at the very beginning in the hotel room instead of knocking him out. Why would he shoot Dean in the shoulder and just leave without making sure that Dean was dead?

Furthermore, when Sam was snatched out of that diner in 2.21 and everyone in that place was dead, how did Dean come out of that unharmed unless there were ~plans~ in the works?

It would just make sense to "kill the spare" (thx, JK Rowling) off right away but no. Time and time again, Dean survives. Even 2.01 shows that the YED could've just let Dean die off and let nature take its course, but no. He made the deal for John's soul and the gun. He didn't have to, but clearly he has his reasons for keeping them both alive as much as he's bothered to.

I'm sure the YED could've had that gun eventually because time is very long and patient. Eventually circumstances would've come up that the Colt would've made an excellent bargaining chip but we'll never know. In fact, the YED has reason NOT to take the deal and let Dean die because well. Dean did kill his son. So. He definitely has plans for both Winchester sons. If they don't tie up the YED arc next episode, I'm sure that's what s3 is going to be about. The Whys and Wherefores.

Dean figures into his plans, definitely. Otherwise, he'd have been toast a long long time ago. In fact, I don't think it's too outrageous to say that Dean should've ended up pinned to the ceiling long before now.

I'm very interested to know what use the YED has for that gun. Why would he even care about a gun and a single bullet?