When USC and UCLA join the B1G, the tradition of the Rose Bowl goes with them. When you think Rose Bowl, you think USC vs. Ohio State or Michigan first and foremost.
I still think it’s only a matter of time until additional PAC schools join the B1G. The PAC will be weaker, thus making it less attractive nationally in a traditional Rose Bowl matchup.
The B1G will play at the Rose Bowl through the season when teams play at UCLA. Also, the B1G Championship Game can relocate from Indianapolis to the Rose Bowl to create a new top game for the venue. The B1G will no longer need the traditional Rose Bowl Game like it did in the past.
For the tradition of the game itself (not the teams playing in it), hopefully the timing of the game will continue as it has in the past. Maybe a B1G (or PAC) playoff team can play there to have at least one traditional school in the playoff game at the Rose Bowl.