How would you get it off with an angle grinder?
Cut inbetween the crank and frame? Or cut the crank?
If a replacement bolt is available, I’d try to drill that out – but the bolt will be tough so that might be hard work.
Otherwise I’d cut through the soft alloy crank with a grinder on one side of the bolt, and then the other if it doesn’t give up.
Again you need the lot secured in a vice, not waving around on the floor.
Before all that I would try heat. Repeatedly get a blow torch on it followed by a bucket of water. Then use a good tool and it might crack off.
The only crank I ever cut off was a well stuck square taper with stripped threads.