If you assume that Abreu will be extended and Reed shows some production, he will at least have a job at DH next season until Vaughn is ready.
At this point, I don’t see a scenario where Abreu isn’t back next year so I guess the key for Reed is tearing it up quickly and how long will Abreu be extended for.
The perfect storm would be Reed tearing it up in the second half, signing Abreu for one more year, and Vaughn being ready after the 2020 season. But I doubt we are that lucky or that Abreu would settle for a one year deal.