All of those contracts between teams that are now going to be in the same conference will simply be void, and the conference schedule will dictate who plays who and when. Those schools will now have an open date in those years (depending on the total number of conference games they'll be playing), and they'll simply have to fill those slots with other teams.
The real tough part will be if you've already got 4 OOC opponents scheduled for 2011, and you play a 9 game schedule in your new conference. Teams will have to buy out the contract for one of their opponents in that case, or they'll have to negotiate playing the game in another year. I'm sure that the Pac-16 would be more than willing to help facilitate the scheduling conflicts in those instances.
As far as the A&M/Arkansas question, that would be up to the schools I would think. If they were in the same division, they would be scheduled to play anyway, so they probably could negotiate a deal with JerryWorld to continue their series in Dallas at a neutral site until the contract was up.