RedirectToAction
, like all the other methods on Controller, is not a terminating call. It simply creates a result that ultimately returns a redirect request to the browser to the given action. Hence you would almost always have it as the expression of a return statement. The return statement terminates the current function. So I would expect this code to save to the given file and then send the redirect back to the browser. The browser gets the redirect response and then sends another GET request to the server for the given URL.
Is this not the behavior you're seeing? If not then describe in more detail exactly what is happening.