IMO, the Bills have a great situation on their hands, four RB's that can play & produce. Currently, the top two RB's are Jackson & Lynch, but the future looks great with Spiller & Bell. I can see the Bills in the Top 5 in rushing offense this year.
I don't know how long Lynch has left on his contract. I doubt he'll get traded by the trade deadline. If this is Lynch's last year on contract with the Bills, then he'll be gone next season. IMO, it would be a big mistake to cut Bell or put him on the practice squad, because he'll get picked up by another team immediately.