I don't see any reason for them to keep a kicker on the practice squad, if Potter doesn't make it my guess is he's cut outright.
I don't see why they wouldn't have room for an extra kicker, they kept Ruvell Martin all year last year for the sole purpose of being on coverage teams. If they can find someone to replace him (Ron Brooks?) I don't see why they can't devote that spot to a kicker instead. Plus, in addition to kickoffs, Potter could also serve as a long FG specialist if the instance arrives.