All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
A Muslim who does not pray should be advised and warned about the evil consequences, both in the present life and the Hereafter, for abandoning prayer. This may encourage him to repent to Allaah The Almighty, Who will consequently accept his repentance, Allaah willing.
However, if you have advised this person and he does not respond, you should desert him.
Allaah Knows best.