It isn't impossible, like you may think...
If Nastya wins the final on Saturday, this would be the rankings:
1 Henin 5791
2 Clijsters 5069
3 Myskina 3848
Remember, that Nastya struggled last summer... all she will be defending is Wimbledon 4R, and US Open QF... which is only 400 points to defend until Leipzig.
Henin will be defending US Open W, Toronto W, San Diego W, Wimbledon SF, Rosmalen F... and that adds up well over 2000 points to defend until Leipzig.
Clijsters will be defending US Open F, Los Angeles W, Stanford W, Rosmalen W, Wimbledon SF, San Diego F... and that adds up to over 1500 points to defend.
Basically, if Nastya can gain more points than Justine and Kim this hardcourt season... she will be #1 by Leipzig. Considering that Kim and Justine have injury issues... Nastya has an excellent chance at accomplishing this.
We've reached the goal of winning a slam... and the next step is getting #1. It's in sight.