How do they replace the Colt?

I think it depends if they ever have to physically or magically have to go up against the demon himself. They know they can get rid of his children with some difficulty, but Mr Demon's supposed to be virtually indestructable. Virtually being the key words. If the demon's that desperate to get Sam then that means that he'll somehow have the means to get rid of the demon. Who knows right? Maybe there's some legends, lore, or a way to know about this is..if there is, we can guarentee the Winchester boys will eventually find it. And they're on the case in their dysfunctional way. So's their friends and allies. And if they find this information..then they can definitely take Yellow Eyes down. Their Dad only said that the Colt was the best bet to kill the demon, and their dad wouldn't have bothered saving Dean if he thought that by bringing him back that the boys wouldn't somehow be able to do something, to win it. Their dad had been at the hunting game longer they have remember? And he knew his children pretty well..despite how much they didn't get along, he had to be pretty SURE to make a gamble like that.

I think it's really going to come down to Sam and the kids like him. The Colt was the only weapon before ... but if the demon's involved in what's happened to Sam and the others, than maybe the demon created a double-edged sword - something that can help but also harm him.

The Ags can stage a "Lone Star coup" in Colt McCoy's first game back

I think Sam is going to develop the power to kill the demon without needing the colt. But it might also be possible that they eventually end up stealing it back.