I've been wondering about trading for Morris is one of my leagues. Obviously, it's hard to trust him because of Shanahanigans, but he has been proven to be at least a consistent fantasy player. Murray has shown flashes, but as you said, is definitely an injury risk. Without that though, Garrett has said that he'd prefer to be a running team, so it's not like he won't get the opportunities when he's back and healthy, but who knows when that will be. I've heard that the foot injury could be a potentially long
I think you get a better WR with Dez. He's definitely looking like option #1 in Dallas (28 targets past two games). I haven't really been following the Bills, but know they've been having some issues. In addition, Dallas has already had their bye week, while I think the Bills still have theirs upcoming, so you get an extra week out of Dez.
I say make the deal. Washington's offense has good potential, so don't mind having two of their strongest players. Also, Sproles isn't a bad RB2 for a bye week.