Hopefully the shutoff valve isn't bad, then you'd be in real trouble.
You say you have a vacuum leak...unless it was a really big leak, the car would still probably shut off with the key. I don't know if the shutoff vacuum is drawn off of the accessory vacuum system or the line going to the brake booster on your car. Mine comes off the brake booster line, and I would think one would have to have a really big leak somewhere to affect that. And then the brakes would probably be pretty bad. It would help to know what car you have.
If the shutoff valve is bad, you could climb under the car and disconnect the fuel lines and just wait for it to die. Make sure the return line stays hooked up. It could take a while to use up all that fuel, but it will eventually kill it. Starting it up would prove to me a pain in the butt the next time however
