If Charlie leaves for the NFL (which he won't), it'll be when the New England job opens up (which won't be for a long, long time).
Parcells and Weis do NOT enjoy a friendly relationship, and I can imagine that Jones will want the next head coach of the Dallas Cowboys to be one of "Parcells' guys". During the Jets/Belichick/Parcells debacle a few years back, Weis was stripped of offensive playcalling duties by Parcells. BP would not endorse Weis, whatsoever.
When Belichick leaves the Pats, Kraft will most definitely put on the Ritz to try to pull Weis to Foxboro. Belichick and Kraft will want continuity in the organization, and want one of BB's guys taking over. At the head of that list was Mangini, but he left for the NYJ (which is why the BB and Mangini relationship frosted over). The other names at the top of that list will be Weis and Crennell.
So if he ever leaves for the NFL, you can bet the house that he'll be arriving in Foxboro, Massachusetts. But he's going to be in South Bend a long, long time.