wow. really good chance the frame is bent. from the picture, it does look like there's a bend by the slider. i'd say you got bigger problems than getting the slider off. but if you need to, cut the bolt and use an extractor to get what's left over out.
Here is my unexperienced opinion (what I would do):
Use something long that slips over the whole slider or into the hole in the slider that is long. Use it to SLOWLY bend the bolt back. If the bolt breaks use a bolt extractor to take it off. If it doesn't break then use a socket wrench....
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