You will be compressing a load of air instead of vacuum. Dive onto an inflated air matress, then an empty one to feel the difference. :wink:
This will resist the pedal, start engine and this will fall to the floor. If the master cylinder has died, a few pints of excellent paint stripper lurks in the servo waiting for you to tip it all over the paintwork. :lol:
The vacuum pump will also have been pumping this into the crankcase, so budget for an oil change too. :?