a person accidentally left my cast iron over a hot burner, and it, well, burned -- a lot of the seasoning seems to have come off, and the cooking surface is more grey than black. How do I save it? Just reseason it?
I think you'll be fine re-seasoning it. Cast iron is pretty indestructible. I'm about to re-season mine. Someone "helpfully" set it to soak! so it got rusty. No problem starting over.
I did the same thing to mine when I walked away from it while drying it on a burner. If you have seasoned it properly, it is just the polymerized oil that has turned to ash. Just scrub it all off and re-season like you just bought it.