Just my opinion, but for Tua to clinch the Heisman I think Alabama has to go undefeated in the regular season with Tua performing similar to his LSU game against MSU and Auburn. If Alabama loses a regular season game, he will need a big game against UGA in the SECCG to win Heisman.
I don't buy that it is over for the Heisman because consciously and/or subconsciously people will always be looking for an alternative to giving it to a player excelling within a dynastic program. If Kyler Murray continues to put up Big-12 numbers and Alabama slips up I will almost guarantee a narrative shift towards Murray's pure stats. Think something similar to how Trent Richardson went from a slight favorite heading into November to a dog against eventual winner Robert Griffin III because of the LSU loss (where TR performed well), the sour taste from Alabama making the BCSCG despite that loss, and a late November big game by Griffin against OU that was ultimately kind of meaningless.
People are fooling themselves if they think Tua has this clinched.