I'd eliminate all humanity and all the dangerous remnants of human society (i.e nuclear plants, radioactive waste, etc) and then let nature reclaim the world and evolution try again once the world had managed to restore itself to a new balance
An old shrink of mine told me that if im still capable of questioning if I've lost my sanity then I havent quite lost it yet. As long as you're able to question your sanity, you've still got it, at least in some degree.