Possible Routes
The New Bobby: The team is trying to transform Garth into the next Bobby. While I love Garth, many fans just sent out an assassination on me, I don't think he should be Bobby. Garth is better the way he is now minus the Bobby traits. He is not over the top like he was in Season 7. Who better to take over then someone who was like a son to Bobby? Sam is possibly the greatest hunter out there with a vast well of knowledge but without the urge to go out into the field again. A Bobby like role would be perfect for him now.
Kill Amelia: This is probably the best way to get him back in the game and stop a lot of fans from changing their channels whenever his flashbacks come on screen. Sam needs a fire lit under his ass again. He doesn't give a damn about hunting right now. The only reason he is hunting is because of Dean and to permanently defeat Hell. If he can stop Hell, we will never see Sam hunt again. Unless, he has a reason to keep fighting. If he has no Amelia, he has no reason to have a normal life. The death of his lover would be enough reason to continue hunting.
Reduced to a Guest Star: This would alienate half of the show's fans though. Sam has finally moved on from hunting. He is going to start an "apple pie" life with Amelia. He will finally complete law school. This would turn the show into Dean's show if it happened. Sam would only return if he was severely needed.
What the Team Should Not Do
Rehash Past Story-lines: No more demon child, Lucifer, or hallucinations. He has moved on from all of that. There is no need to explore anything from those old story-lines.
Getting Rid of Him: Either by complete retirement or permanently killing him. If he was reduced to a guest star, we know he would appear from time to time. Permanent death would destroy the show.
Continuing What He is Doing Now: Smallville did to Clark Kent what Supernatural is doing to Sam for 2 and a half seasons. It nearly killed the show for many fans. If one of the show's main characters isn't going to be developed, why keep him?
Double Edged Sword
Possibly Replace Him: Another change-up that would anger fans more then when the People's Choice Awards ignored SPN's win. Replacing him is an extremely tricky problem. If a new, interesting, and likable character replaces him, then try that character out for one season. If it destroys the ratings, then bring Sam back but with a real story-line. I have faith that Jeremy Carver has something planned out for Sam. It is his style. He builds up then explodes. See Season 2 of Being Human for proof. Make sure to comment and share your thoughts on this topic.