Continuing this thread:
What remains in the calendar is 2 250s, 1 500, Paris, and Turin. Those who will be partaking in next week's 250 are already signed up, so the new elimination point for YE#1 is 3250 points less than Alcaraz - so mathematically only people with 3210 points or more have a chance at #1. That's Alcaraz, Nadal, Ruud, Tsitsipas, Medvedev, and Rublev.
Realistically, like I've outlined before, we're down to Alcaraz and Nadal. Alcaraz has confirmed Basel, Paris, Turin. Nadal hasn't confirmed any as far as I know, but I anticipate at least Turin. I do not expect Nadal to play any 250s or 500s.
With that said, Nadal is 650 points behind Alcaraz. If Nadal plays only Turin, he would need to reach at least the final to have a chance of getting ahead of Alcaraz, and Alcaraz could secure YE#1 with 855 points at Basel, Paris, and Turin combined. Very reasonable. Ultimately, it depends a lot on if Nadal plays Paris and how well Alcaraz does before Turin.
If Nadal only plays Turin: Alcaraz as good as has the YE#1 already. It would take an incredibly bad collapse to lose that. Not entirely on Nadal's racquet.
If Nadal plays both Paris and Turin: Also not entirely on Nadal's racquet. He couldn't guarantee a YE#1 finish with a Paris win and Turin win - 2500 points. Alcaraz can win 2100 (so could still lead Nadal by 250 points) but a poor result in Basel for Alcaraz suddenly means the YE#1 title is in Nadal's hands. Even so, I still anticipate Alcaraz is in pole position, but it's more up in the air.