Either a drill or angle grinder would be the tools of choice there, Vic. Since you have no need for the bent grate, the grinder would likely be quicker.
If you have a plastic drain, the grinder might make more heat than you want unless you're very careful. But being a surgeon and all, you shouldn't have any trouble with that, eh?
Actually getting the screw out of the hole is another matter. While it's possible to drill some bolts and use an "easy-out," the bolt you're dealing with is gonna be too small for that unless you are pretty accomplished at the procedure.
It's possible that if you grind off the head you'll still have enough shaft to get holt of with vice-grip pliers. Or not.
Might also be that you can drill new holes for the grate attachment, depending upon what you're working with.
My opinion; worth price charged.