If we want to stand a chance of signing him, we have to do really well in the PL this season, not just 4th place. Reus' next destination is going to be a club where he thinks gives him the best chance to win trophies. Reus stated that he considers himself not a talent any longer and that it's time for him to win trophies. Of course nobody can guarantee this, but considering that we'll most likely face competition from Bayern, Madrid, Barca, the only way to convince him to sign with United is to convince him that he can win trophies at United.
I typed 'win trophies' a lot.