The team could play really well for the remainder of the year, and they still may finish 2-2. In that case, I think he stays.
But, if they lose to Vanderbilt, that would mean that the players have flat out quit on CJP. While I don't think it will happen, A 2-8 season with a completely uninterested effort from the players for these last four games MIGHT force Fulmer's hand. He doesn't get to make this decision in a vacuum. Keeping his job demands keeping the money flowing.
At this point, the cost of firing Pruitt should not be looked at as the total cost of the buyout, but rather the cost of firing him this year versus firing him next year. Unless there are some unknown, tangible reasons for this regression of almost every player on the team that are easily correctable and beyond Pruitt's control, there is absolutely no reason at all to believe things will somehow just get better. So, if that cost is 4-5 million, an argument could easily be made that keeping him for another year could cost them that in ticket sales and booster support.
At this point, it feels like it is not a matter of "if," but "when."