[curtis73]

It would start, and provided your foot was on the brake it would just idle in gear. Most transmissions would wait a second to drop in to gear since it takes hydraulic pressure to engage.

I had a I/O boat that was stuck in forward. I would start it and it would start moving. Things would be very similar in a car.

However, for safety reasons, all neutral safety switches are designed so that if they fail you can't start the car at all.