He would almost certainly win the nomination if it were today, but three years is an eternity for another candidate to get attention, and I think it's more likely than not that the 2024 nominee is not Trump.
That's mostly an actuarial question. Donald Trump is a vengeful man, and if he could take it out on people who thought him unfit to be President despite being the Most Wonderful Person Who Ever Lived, his character suggests that he would.
Three years is an eternity with someone at his age with such previously-existing conditions as obesity, bad eating habits, physical inactivity, and an inflexible mind.