Hi there.
Not sure which part of the world you are in, but here in SA, as soon as the water had evaporated, the M&S lights on my vehicle stopped flashing.
Also, with the M&S lights flashing, the car should be at least useable as it is in Limp Home mode, where the only gears used are reverse and 3rd.
Perhaps take it for a small run and build up a bit of heat in the gearbox then leave it for a while. The heat should dry the switches, assuming it is a damp gearbox selector swich. Obviously, check fluid levels etc for any other problems before taking it for a drive.
Good luck.