...Where Florida State or Alabama might have played Murray State or Austin Peay, maybe now they will go more for BG, Tulane, or even a historically weak P5 like Wazzu or Indiana. I think it will be mostly business as usual for the back half of P5 schools who know that they will still want to just get wins any way they can.
You raise a great point. It seems likely that the FCS schools will take a major hit. A win over BG or Tulane may not help Alabama much, but it will still mean much more than a win over Murray State or Tennessee Tech. I can easily imagine the P5 schools reducing or eliminating FCS games, but still wanting/needing 7-8 home games, and thus continuing to buy G5 games.
If this is right, and I suspect it is, now that I think about it, the G5 schools will end up about where they are. They will still be able to get paydays from money games, but they will have some extra expenses from increasing the scholarships to cover out of pocket expenses. Meanwhile the FCS schools will really get hit hard, losing most of their big money game deals with P5. There will still be a few money games paid for by G5 teams like Ohio, but there will be a lot more teams looking for them than there are G5 teams buying games, so the price could very easily fall.
We've seen a huge rush of schools in recent years trying to escape FCS, where the economics have all the negatives of Division I without any of the positives. That seems likely to increase.