I cannot think that will last much longer with the quality of teams they will have.
But- I mean- none of the teams are leaving right away. I think even USC and UCLA have another couple years unless I am mistaken.
This season is the last one in the PAC for both. I think it's the same for the others that are leaving as well.
As for the P5 designation...I'm not sure how that works. Even is Stanford, Cal, Wazzu and Oregon St stay, they're not much, if any better than the MWC schools that would come in with a merger.
But I haven't come across anything about how a conference can lose that designation.