That is always possible. Right now the Big 12 doesn't have any more programs with a high likelihood of being poached. PAC 12 has everyone looking for a spot in the Big 10 or SEC and some programs like Oregon, Cal and Stanford probably have more of a chance of doing so in the future than any Big 12 team. So the Arizona's, ASU's, Colorado's, and Utah's of the PAC 12 may be tempted to gamble on a move to the Big 12 if they see a near future without Oregon, Cal, and/Stanford along with USC and UCLA in the PAC-12. Those aforementioned schools like Oregon may also be tempted in that if they see the PAC-12 losing 4 of its middling programs then they risk being stuck as independents or in a defunct conference for too long waiting for further Big 10 expansion westward.
Big 12 isn't great, but honestly it is the most stable conference outside of the Big 10 or SEC if only because the Big 12 lacks any programs as lucrative to poach as the PAC-12 (Oregon, Cal, Stanford) or the ACC (Clemson, FSU, Miami, UNC, UVA). That is why middling teams in the PAC 12 that do not see high hopes of joining the top 2 conferences may see the Big 12 as the most stable of the remaining non power 2 conferences. Even if they just want to use the Big 12 as a stepping stone to one of the bigger conferences later.