I personally don't think Buffalo is the most likely destination for Rivers, though I don't think any of finfan54's reasons necessarily rule it out.
If available, Buffalo might draft Kenechi Udeze or Will Smith at #13. They might even consider drafting Tommie Harris and playing him at LDE, but if those guys aren't still available (or if Will Smith doesn't fit Buffalo's need at LDE in the eyes of the Bills) there are really no other linemen who represent value at #13.
I don't think the Bills regard Mike Williams as a bust. I think they know the offensive line coaching has sucked for years. A great line coach like Jim McNally should bolster his play along with every other lineman. In any case, after Gallery and Andrews, the next offensive lineman worthy of a first round pick is probably Vernon Carey who is a late rounder, a reach at 13.
I'm not sure who finfan54 thinks will be a "splash" pick for Buffalo. Reggie Williams could make a splash as a rookie. He may or may not be available at #13 and a number of mocks have Buffalo taking him. Udeze is another who could. We'll just have to see.
My personal opinion is that Buffalo is more likely to sign a free agent QB or pick one in the second to fouth rounds of the draft than to pick Rivers at #13.