Extradition and rendition are two completely different things. If the CIA wants to rendition Assange, it'll just happen. It's an extrajudicial process more akin to kidnapping than anything else. If anything, the arrest warrant would just get in the way. It's hard to disappear people out of western European jails--easier to just grab him off the street, be it in London or Quito.

If the US wants Assange extradited, they would have to play by the rules. And the rules don't help at all if Assange is in Sweden.