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The driveshaft wouldn't be snapped from the downward force. It would be snapped because it's happily spinning away at probably a couple of thousand rpm and then suddenly the rear tires make contact (assuming this is a RWD vehicle, otherwise it would be the CV joints breaking for the same reason) and try to get traction and move the car forward, but rubber is made to stick the surfaces and there would be an astounding amount of force applied along the drivetrain that was sped up to 100mph with no resistance suddenly trying to instantly accelerate from 0mph to 100mph with a very considerable amount of resistance.
I don't think the driveshaft rotation would be in the thousands, as the rear diff is a 3:1 ratio, and the wheel diameter further effectively increases the ratio. Driveshafts are suprisingly slowly rotating parts.
But I still agree it would likely fail, as the weakest element in the drive train.
A pretty typical 5th gear transmission ratio is somewhere in the 0.75:1 (engine rpm: transmission output shaft rpm) range, meaning the driveshaft would be rotating at somewhere around (definitely plus or minus) engine rpm. My subaru cruises at 50 at somewhere around the 2k rpm range, so the driveshaft would be spinning at a similar rpm. The diff pinion to ring gear ratio in the differential slows things down quite a bit so your wheels aren't spinning at engine rpm anymore.