A little odd reasoning here. Looking at points to defend is not very meaningful. The real point is that Fed is currently 1000 points behind. What he needs will depend on what Djokovic does. Playing Shanghai will definitely leave him closer in the race before Basel than not playing Shanghai would.
yes, I don't understand why Slasher doesn't look at the Race (Fed 1105 points behind), it's so simple comparing to looking at points to "defend" and so on.
I'm convinced that Fed will not play Paris and Djokovic will, that's why imo, Fed needs to do something great in Shanghai to have a chance for the YE #1.
Will it be enough or not ? too early to say, it all depends on what Djokovic will do and what will happen in Basel and the WTF.
Besides, as far as the rankings are concerned, getting to QF in Shanghai would guarantee Fed to stay number 1 until the end of PAris-Bercy, that means 302 weeks at this rank instead of 299.