After today Fed is only 140 points behind Delpo in the race. Given Delpo just injured his knee, I expect Fed to tie it up at Basel, and the battle for #3 is likely to be decided at the WTF.
First of all he needs to go deep enough into events to play the top seeds aka Delpo and Novak, and give them a good run even if he loses. The damage is done for this season but he can make some amends by gathering some momentum into next year. See 2013 for example, he lost a heartbreaker to Delpo in Basel, but he avenged his loss and had good runs in Paris and WTF (a set and a break up against Novak and grinded a very important victory against Delpo in the RR stages), that gave him belief that he could still do it in the next season.
I hope Fed plays Bercy this year, he's barely played any matches unlike last year. And there's a week gap before WTF anyway.