I fully believe that they'll insist on the GOR being short (5 or 6 years, but that's what the PAC wants anyway).
And I fully believe that before signing a short GOR, they'll reach out to the B1G again to make sure there's not an invitation forthcoming.
But if the B1G tells them they might get an invite later, but not at the moment, then they just don't have a lot of options.
1. They could sign a short GOR with the PAC...which would (worst-case) delay their entry to the B1G by a few years
2. They could defect to the Big 12...where they would have to sign a GOR for the same length, plus be assessed a hefty exit fee when they leave
3. They could go Independent and try to arrange their own TV deal
4. They could refuse to sign any GOR... Which would torpedo the PAC deal, causing other PAC teams to defect to the Big 12 and leaving them with the options of either 2 or 3, just with more steps