The OP's not necessarily down to that last resort. If the OP can get some penetrating oil into the threaded joint to lubricate and loosen the seized threads, as Bill Kapaun noted previously he can still use a pair of locking pliers (e.g., Vice-Grips) to remove the stripped nipples. Doing that will be a bit of a pain, but it will preserve the spokes. (He'll of course have to replace the mangled nipples.)

That's what I'd try before cutting the spokes, anyway.