I think Nadal would get World number one back If Roger federer skips Dubai and Rafa wins Mexico title that would put nadal 100pts ahead even if Federer wins next week.?
No. If Roger wins Rotterdam he'll be 600 points ahead of Rafa going into Dubai/Acapulco (with those points taken off), which means he'll be #1 at least until Indian Wells.
So let's say Roger wins Rotterdam, skips Dubai, and Rafa wins Acapulco. Roger's +100 going into IW. After IW points come off, Rafa goes up +810 as Roger loses 1000 points and Rafa only 90. The differential increases by another 400 after Miami, so the gap would be +1210 to Rafa without new IW/Miami points. Of course then Raf has 4680 points to defend during clay season, so unless Roger struggles now
and Rafa does at least as well as last year, Roger will almost certainly be #1 (again) during clay season, at least for parts of it.
But let's see how Roger does at Rotterdam first - there are some tough opponents and a title is not a foregone conclusion.