There is a lot of ways this could shake out, but just because their is no more PAC does not mean no more Rose bowl. It would just be B1G against someone else or something like that.The Rose Bowl is a sacred cow to the B10 and they likely aren't going to blow up that relationship by adding any P12 schools.
The new B10 deal will be disclosed this summer and how that deal shakes out will then set up the most likely available options for the P12 who is next in line with their deal expiring after the 2024 season. B12's deal expire after 2025.
There is a lot more money at play than just the Rose Bowl.