All open files, up to the most recent 21 (and that could be increased) are in the recent file list.  Clicking on any name loads that file, unless it is already loaded.  The exception enforced in filelist.FileList.open, lines 29-32:

        if key in self.dict:
            edit = self.dict[key]
            edit.top.wakeup()
            return edit

I believe that we just need to ask, before the return, "Replace editor content with file content?" and if yes, call edit.io.loadfile(filename).