I imagine that it wouldn't be difficult to find a few attorneys willing to argue that there never was an official notification to leave the conference. The negotiations on this should keep the law firms representing each side well fed for a while.
I also wouldn't be surprised if SDSU tries to get the state government involved, using the possibility of a catastrophic situation (having no conference for any sports) to influence the P-12 to add them.
We should get some clarity on all of this with the next dozen days but it may take some time for everything to shake out.