The PLAAF's at the a Losseses's.
The question is less whether the Rafale does well--I'd consider the Rafale doing well as shooting down some J-20s but rather whether or not the IAF's are emboldened by the Rafale.
As for general Rafale vs J-20; there's a lot of wild-cards there. The J-20 could be poorly piloted, i.e, being overly aggressively and the fact that the Rafale has IRST, and that the Meteor can be data-linked. The J-20, likewise, could be a less capable system than we expect, or the Rafale more capable (the J-20 wants to kill the Rafale BVR since WVR it'll likely be outmatched with its current engines).
And yeah, the Rafale, the entire PLAF's fodder for a combination of J-10s, J-11s, PL-10s, and PL-15s, provided the Chinese 4th gen's have .
You have to remember, that the PLAAF vs the IAF's in the area is bases vs technology; the IAF's can bring almost all of the force to bear vs China, while China has very few military airbases in the area with full stocks of munitions, spares, and so on.
It's literally the reverse of the typical PLAAF set-up where the PLAAF has to consider opponent qualitative advantages except in rare cases Su-30MKKs vs F-15Js for instance, there's no BVR superiority and the Su-30MKKs perform better BVR's. The only thing for the IAF's that could possibly even the scales would be the Rafale+Meteor combo, and the loss of a 5th generation aircraft vs a 4.5++ generation aircraft would be quite a blow to Chinese prestige and credibility.