They took Mike White in the 5th round. At this point that should be enough resources to develop a backup. I think that's personally the route to go with backup quarterback. A guy hungry guy. Not a retread. We've been done that route with Weeden and Casell.
I prefer young backup QBs over journey veterans.
Occasionally a team has a Foles type backup that can win games; however, most often the Cowboys are going to lose if the backup plays more than a game or two regardless of whether it's a journeyman veteran or a young QB.
I do wonder if Mike White can't beat out Rush in this training camp if White really has what it takes to be worth keeping.
Rush appears to be having a really good camp from everything I've seen and heard.