For the short term, at least, Trammell has said Uggy will keep closing games and Percy will work himself back in non-save situations.
Beyond that, there has been no committment from anyone, so everything here is speculation.
My own 2 cents is that it will be hard to yank Urbina out of that role unless he has a couple of rocky outings (and at the same time Percival pitches lights-out). Trades and injury relapses blow up everything, and none of us can make that call now.
For fantasy, I'd hang onto both and keep the fingers crossed.
As everyone else said, Urbina will remain closer for now. Considering our manager here in Detroit, Alan Trammell has shown to handle things in strange ways, it's anybody's guess how the situation will be result if Percival can prove he is once again healthy and effective.
I also stick by my opinion from before the season began that the Tigers will be hard-pressed to trade away Urbina as long as a .500 record remains in reach. Unless they get some desperate team to overpay, they will hang onto him, since he is the best thing going in the bullpen.
I believe Urbina is being showcased to the Giants, Cubs, D-Backs, etc. He may not relinquish the role until he is traded. Sucks for me as I used my #4 WW priority on percy about a week ago.
Urbina is still worth a spot, but I'd trade him if you can. Percival will return as the closer, unless he totally sucks out. They would be quite happy with Urbina as the setup man, and Percy closing. Or trading Urbina.