With Proof and Em both gone...probably not.
If they brought Royce in, I suppose I would give them a shot.
However, I do believe that another D12 with Eminem album is possible, after R2. We may be experiencing the second coming of the Eminem Golden Age. Release a whacked-out, demented album. Come back with a superior album. Drop an album with D12. One more solo album after that (hopefully) that's different than the previous two but still a classic.
Well...we can dream, anyway.