There are many definitions of c - it appears as a constant in many different physical equations. Right now, all of these definitions are consistent. If you have a new physics where all these definitions remain consistent and you can still transmit information faster than c, then certainly I have lost the bet. Other cases would be harder to settle - I did state that weird physics along the lines of "this is why photons are slowed down in a vacuum by dark matter, but neutrinos aren't slowed" wouldn't win the bet.