I'd be very surprised if the result was overturned in favour of Lewis this evening, as that would also entail, of necessity, the resignation of several FIA officials.
Mercedes' options will then be to sue the FIA, and / or seek an injunction on the result of the season. On the face of it, they would seem to have a strong case, but RB would also defend their position strongly. However, if it did get to this point, and the same FIA officials are in place at the start of next season, it will be interesting to see how Mercedes proceed at that time. This could drag on for some time. A shame, as it could have been avoided by better race control.