answer me this.

how does that call go?

tom: hey, we just got a big12 invite that we're going to accept unless you offer us an invite.
larry: sorry. aint going to happen.
tom: thanks, bye.

or

tom: hey, we just got a big12 invite that we're going to accept unless you offer us an invite.
larry: yeah, we'll invite you.
tom: thanks! bye.

or

tom: hey, we just got a big12 invite that we're going to accept unless you offer us an invite.
larry: yeah, well, i'll have to talk to the guys. i'll get back with you.
tom: thanks! bye.

i think it's either "sorry, no" or "we'll get back with you." would you be willing to wait for him to get back? i wouldn't risk it.
if the pac12 wants us, they'll invite us. i guess if we're in the middle of being "interviewed" by the pac12, then maybe we could fill them in, but if we aren't, just say "yes" to the big12 with no delay.