McElwain may or may not be it. Time is running out and UF's will begin hemoraging fans and revenue without a better offense. If he fails to improve the offense as he was hired to do, then eventually he will go the way of Les Miles at LSU.
Still the new AD will be very slow to fire Foley's football hire. If he fires him, the new AD puts his own job on the line.
Also the SEC East is still stocked with DCs trying to play head coach. So I expect UF to win the East again next year. But will two straight SEC East titles with 100+ offense make McElwain almost untouchable now, another SEC East title with a bad offense oddly makes him more vulnerable. As I said above, he was hired to fix the offense and win. If the offense remains awful he will eventually go. We will not know that for another year or two.