Is it permissible for a Muslim to return the greeting of one who abandons prayer, or to host or visit him?

One must advise the one who abandons prayer, invite him to it, and explain the greatness of prayer's status and the punishment for abandoning it in this world and the Hereafter. It is also fitting to visit him and host him if that helps in his rectification. He should only be shunned if it is highly probable that shunning him will be a cause for him to return to prayer.