If you actually depressed the clutch and forced it into reverse the first thing you would experience is a bone shattered racket of mangled gear cogs from the gear box. The drive shaft will have sheared, and if you are lucky, not come up through the floor or through he bulkhead into the cabin, if you are in a front wheel drive car you would probably lock then shear the drive shafts to the wheels, go in to a spin and have written off the whole car as replacing engines, drive trains and gear boxes are v expensive.
Enjoy the ride!