Mathematically:

Assuming no more than 1 500 in stretches without many 1000s or above AKA: February, June, we can come to a conclusion.

Dubai/Acapulco/Rotterdam/Rio: Assuming Novak doesn't play and Nadal wins, Nadal lowers the gap to 2135.

Indian Wells/Miami: Since this is mathematical, Nadal wins here and Novak loses R1. Nadal lowers the gap to 135.

Monte Carlo: Nadal cannot gain points, but Novak can lose 90. Gap lowers to 45 points.

Barcelona: Gap impossible to increase.

Madrid: Nadal lost in QF in 2018, so the gap can be eliminated. Nadal gains 820 points and Novak loses 45. Gap is now 820 points in Nadal's favor.

Novak holds #1 until Madrid, mathematically.

Assuming, however, Nadal wins and Novak is a semifinalist in every single event, it becomes a conservative approximation of a "realistically secured" amount of time, accounting for upsets and whatnot.

Dubai/Acapulco/Rotterdam/Rio: Still assuming Novak doesn't play and Nadal wins, Nadal lowers the gap to 2135.

Indian Wells/Miami: Novak gains 720 points, but Nadal gains 2000. Gap = 855.

Monte Carlo: Nadal cannot gain points, and Novak gains 270. Gap = 1125.

Barcelona: Novak played last year, so no reason he won't again. Gains 180 points. Nadal stays the winner. Gap = 1305.

Madrid: Nadal gains 820 points, given the QF last year. Novak gains 315. Gap = 800.

Rome: Surprisingly, this one doesn't change at all.

RG: Nadal gains no points, but Novak gains 360 for a semi instead of a quarter. Gap = 1160.

Queens/Halle: Novak loses 120 points. Nadal gains 500. Gap = 540 points.

Wimbledon: Novak loses 1280 points. Nadal gains 1280 points. Gap = 2020 in favor of Nadal.

So realistically, Nadal has no chance of catching up to Novak until at least Wimbledon. If we make it so Novak makes finals (more liberal estimate), then Novak still leads by 320 points by Wimbledon, and Nadal can't overtake him until at least Cincinnati.