Surely Ferrari's only hope is to gamble on a wet race and just totally set the car up for the wet to the detriment of their qualifying (assuming qualy is dry).
Well, realistically with them saying there is a 100% chance of rain on Sunday, the gamble would be setting up for a dry, even if qualifying was wet, and pray for a dry race rather than the other way around.
But lets say its going to rain, and Alonso gambles and goes for a slow set up, if it starts wet, then they all get to change tyres anyway don't they, and while they might have less downforce, Alonso could be so far back with comprimised qualifying that no amount of good starts will help him. Even if Vettel DNF's, he's still got to be very high up the grid. Alonso can't afford to gift qualifying away. If it starts off dry, then rains, then Alonso will likely be painfully far back by the time rain happens.
If it starts off wet but drys off, Alonso is boned also. Basically with the chance of rain being stated, the vast majority aren't going to go for a perfect dry set up anyway, most of the grid will play it safe, and so will Vettel, because he has a car that eats everything but the Mclaren alive anyway, he doesn't need the fastest car in the dry to win the title, so he can afford to go high downforce, wetter setup and even if it doesn't rain, that car is capable of qualifying on the front row and doing well in the race.
If Vettel doesn't DNF< I can't see Alonso winning it(unless Vettel gets damage in a collision), if he does DNF, Alonso has to have a car competitive enough to get 14 points, throwing qualifying won't get him anywhere.