1992 Honda Accord replaceing waterpump

You could try drilling it out? It may depend on how big the screw, as far as how easy to get out? Your local auto store should have an" ease-out" tool. Made for removing broken bolts.

If the screw is big enough, use a left handed drill bit, if the screw tightens to the right. Use reversing electric drill. If you get it out, you can try cleaning the threads with a tap/thread chaser.