I don't think the Bills FO would have traded Peters if they felt they could'nt fill the void with players already on the roster. You know they didn't talk about Peters for an hour or two, it was the topic for weeks. I believe they convinced themselves that they can still go forward with their draft plans, in lieu of trading Peters. I just can't imagine they said "well we don't think we can solve the LT issue in house, but lets trade Peters anyway and hope this LT is there at #11 or this LT at #28", etc.
I believe they are going to draft Pettigrew. I think they believe he is the best player at his position by such a large margin that it warrants taking him at #11. I think they feel drafting a DE or LT will reduce them to the 3rd or 4th best player at either position. And that the argument for drafting Pettigrew at #11 is more justifiable than taking the 3rd best or 4th best LT or DE. The 11th pick is just too high to not draft the best or second best player at a position.
Now in saying all that, I am now officially deciding that Pettigrew is the player I hope they draft. I made a comment earlier that I could argue a pass catching TE could do as much for our pass coverage issues with Peters gone as a blocking TE could. Well Pettigrew can do both and do both very well. I feel comfortable saying Pettigrew can play every down.