"MUSLIMS" : How would you guide someone who is planning to leave Islam?

Talk to him and know what he is confused about. There is a solution to every problem and you may take him to a good scholar. Tell him, life is very little even if he may think is a long one. If he sees some worldy gains in some others. The eternal world with Allah is far better for believers. Unto Allah everyone return this day or the other. Also Pray for his guidance.