The Arizona Wildcats and Arizona St. Sun Devils are uncertain of what will happen to them if the conference does to choose the path to expand to 14 and 16 teams. Currently the Oklahoma Sooners and the Oklahoma St. Cowboys have their eyes westward, and it's likely if they choose to go in that direction, the Pac-12 will be ready to accept them.
The big question is whether the Texas Longhorns (along with the Texas Tech Red Raiders) decide to come along. If they do, the Pac-16 that conference commissioner Larry Scott originally envisioned a year and a half ago will have come to fruition.
In either case, both Arizona and ASU are likely to see big changes in their current divisional structure. Both schools are currently situated in the Pac-12 South. If it's only Oklahoma and Oklahoma State joining up to create a Pac-14, then divisional alignments would not likely be satisfied along traditional geographical arrangement. The most likely alignment of two divisions would be created along a zipper format that splits traditional rivals. So it would go something like
Pac-14 Division A | PAC-14 Division B
Arizona | Arizona State
California | Stanford
Colorado | Utah
Oklahoma | Oklahoma State
Oregon | Oregon State
UCLA | USC
Washington | Washington State
This is only a hypothetical construct (I don't imagine Division B would be too thrilled with their opponents in Division A), but you can see that Arizona and Arizona State would no longer play along conference lines. They'd still have their rivalry matchup, but everything else would be geographically in-congruent.
I'm guessing that because of the concerns about a Pac-14, Scott eventually desires a Pac-16 with or without Texas, so it's likely that he'll go after schools like Kansas, Kansas State or Missouri to find the additional two members. That sort of division would likely fall along traditional geographic lines, and would place Arizona and Arizona State in the same division. However, they'd likely be separated from all their original Pac-10 members in a division with Colorado, Utah, Oklahoma, Oklahoma State, and two other schools.
To discuss the Wildcats, head to Arizona Desert Swarm. To discuss the Sun Devils, head to House of Sparky. For more discussion on conference expansion, head to Pacific Takes (the SB Nation Pac-12 site).