I suspect the Highwaymen are just cannon fodder. As you say, ridiculous idea but it was an easy way to introduce a few new faces. They will give us a couple of episodes of them hanging about in the background, then I'm guessing they'll end up helping build the new fence marking out Whisperer territory in episode 15. Might just save one or two of the better known characters, though I still reckon Ezekiel has had his chips - he seems far too happy and that's never a good sign in TWD.