First of all, they're shocks on that car, and secondly you're never screwed

There are several ways of getting it off. The top of the shaft itself should have a flattened spot for a wrench. Get a proper sized wrench on it and on the nut. Vice Grips are for welding
Short of that you could cut the nut off with a grinder or cut off wheel.
Most shafts are installed in the shock valve with threads. Just keep on loosing the nut (turning the shaft) until it pops out. It may be rather explosive and messy since the nitrogen charge will splatter smelly oil all over the place.
You could go to the parts store and buy a nut splitter to get the nut off.
Tons of options.