From the Jim Lee panel at the Baltimore Comic-Con, via Newsarama:
"The Highwaymen will conclude its arc and then end, Lee said, noting that the series was a great read but hasn’t performed well sales-wise. After the series is over, Lee said that they’ll be working with the creators again."
Well, there you have it. We're glad we got to tell the story we set out to tell. If you find us at a convention bar one of these years, we'll tell you what would've happened...if you buy us beer. And nachos. Definitely nachos.