Sorry for being too pedantic but found couple of errors in your calculation.Full thoughts and notes!
How Close Is Daniil Medvedev To World #1?
Djokovic- 12,133, defends 400 pts from Finals, 1000 pts from Paris, 180 points from Shanghai, 23 points from Indian Wells, 500 from Tokyo, and 90 from Vienna, defends 2193 until end of year = 9,940 + whatever he does the rest of the year
Medvedev- 10,780, defends 1500 pts from Finals, 1000 pts from Paris, 1000 pts from Shanghai, 90 from Vienna, 250 from St. Pete, 23 from Indian Wells = defends 3863 until end of year = 6,917 + whatever he does the rest of the year
Djokovic has 3,023 point cushion over Medvedev in the ranking for the rest of the season
Medvedev can get 10,417 with a sweep, 10,917 if Vienna as well. Djokovic must score 477 points to cover the 3 title sweep, and must score 977 points to cover the 4 title sweep.
What will they play rest of year? My prediction is Paris and Turin for Djokovic only, and probably Indian Wells, Paris, and Turin for Medvedev. Vienna is an option for both as well for an extra 500 points
Only 1990 point cushion in the race to #1. ATP has said the YE #1 for 2021 will be whoever gets the most 2021 points but the computer ranking #1 would be who is still #1 on the rankings that are still partially COVD-affected until August 2022.
For me and my numbers, whoever is the ranking #1 is who will be the YE #1 as well. Hopefully we do not have a controversy where Medvedev scores the most 2021 points but not enough points to be the computer ranking #1. What a mess that would be!
Medvedev would have to outscore Djokovic by between 1990 and 3023 points to have a "split" #1. More than 3023 and he is #1 with no controversy, and less than 1990 and Djokovic remains #1
From the 10780 points in the current official tally of Medvedev, the 23 points from IW are not countable and therefor shouldn't be deducted. In addition, he has 10 point from Rome that are not countable.
These points (IW and Rome) will become countable after points from St. Petersburgh and Shanghai drop (St. Pete's points drop next Monday)
Djokovic on the other side doesn't have as many tournaments played and his IW points are countable this week.
Therefore the number of points Djokovic is not defending this year is correct - 9940, while Medvedev is not defending a total of 6950 points. As result, Djokovic's cushion is 2990 instead of 3023 points.
Last but not least, you don't need to calculate the points each player is not defending, but simply go to ATP Open Era & Live Rankings and deduct Djokovic's and Medvedev's points by 23 each (Slasher still has March of 2022 as a drop date for the IW points)