I do think it is possible the Rams keep Bradford on the roster next year, but there are a lot of influencing factors:
1. Do they get a top QB talent in the draft? If they draft high and get a top QB, it will factor in to the decision.
2. How well does Davis play the rest of the way? He's a backup at the least, and much more affordable than Bradford next year.
3. How quickly does Bradford's rehab go? Second injury to that knee, even Sam may be traumatized by it and afraid to push back too quickly.
4. What would they project the trade market for Sam to be? There will be a few teams that need a quarterback in the first part of the season, always is.
My guess is that Snead trades Sam. Reasoning is he does have some value and upside still, but the Rams cannot afford to risk going with him any longer. The Rams will draft a QB this year, and it's gonna be a young group with the draftee, Davis, and Gilbert all competing in camp for the starting nod. Sam doesn't fit that direction, giving him snaps when he's not the future is just dumb.
If I had to put percentages on it...
50% they trade Sam (this would mean they keep him on the roster maybe into the season)
40% they cut Sam (any time from offseason on into camp)
10% they keep Sam (he serves as the backup to their high draftee)