Same as 2016: plenty of voters, convinced the split will guarantee a Biden win, reluctantly vote for the Dem nominee and choose the GOP congressionally to quench their lust for "tsheks and ballunces".
The only people unironically entertaining the possibility of a "1912 redux" in the event that Trump were to run as a third-party/independent candidate are hardcore Democratic partisans/hacks who have shockingly little understanding of how poorly an emasculated, whiny loser like Trump would perform among Republican/-leaning voters in a competitive general election between Biden and an actual Republican challenger, esp. a competent one like DeSantis.
Stop creating these ridiculous caricatures of Republican primary voters and get some fresh air.
Forgive us for being skeptical that Republicans finally see Trump as the "whiny, emasculated loser" he's been since 2015. You've been led by the pied piper for 7 years and if if the polls are true indicating 50% of the GOP still believes the election was stolen, then what has fundamentally changed?