I based my assumption on the fact that the Athletic Department is currently self-sufficient (the Church doesn't pay the bills in any way for sports right now). Is it possible that the Church would choose to pay the bills for the short term to put the AD in a better situation in the future? Absolutely. But to me personally, I don't see that as 100% guarantee of happening, even though I admit that the odds of it happening are probably fairly high.
I also don't see a way that the Big XII would allow us to keep our current tv deal in place. That would give us six home games (including at least 3 conference games) that couldn't be broadcast under the current Big XII deal. That deal includes games on ABC/ESPN and Fox networks. Why would ESPN continue to pay us 500k or more for each of those home games when they could just option that game to one of their current TV partners? If they did keep paying us individually under our current contract, they would be essentially paying twice for the same game between the two contracts.
Donors are obviously a possibility and I would personally have no problem making donations or paying increased season ticket prices if that was what it took to get us an invite into the Big XII as mentioned in the poll, but I don't know if all BYU fans/donors would feel the same way. Afterall, BYU fans are generally stereotyped as being extremely "frugal."