I hope nobody ever tries to do that My guess is the motor would last about 5-6 laps with that kind of bind in the drivetrain.
actually, it's quite common to use different ratios f/r. the xxxs has a few pulleys for that very reason. also, many carpet racers will run a few, or more, packs w/o cutting their tires. typically the rears can become upwards of .050" larger in diameter than the fronts. it's not as significant as the internal ratio change, but i believe either configuration will last the length of a 5 min stock race.