It happens. People sometimes wander away from God and their convictions. In the process, they make a real mess of things.
When you see people do this, here is how you can respond....
1) Stay humble. Remember you are no better than them. We all are sinners and we all are capable of wandering away. So don't get cocky and say, "I would never do what he did!", because you don't know that for sure.
2) Pray, and then pray some more. Ask God to grab their attention and change their heart. Ask God to rescue that one who is caught up in sin and not thinking right. And don't give up on praying. Just keep lifting that person up to the Lord. Amazing things happen when people pray.
3) Reach out in love. Contact that person, and let them know you still care about them. Obviously, you don't like the sin. But you should still like the sinner. Tell them you are concerned. Tell them you are willing to help them make changes. Just go after them and try to help.
4) Celebrate their changes. When they come back to the Lord and get their life back on track, be happy for them. Rejoice! One of your brothers or sisters has returned, and that's a wonderful thing.
5) Be their friend. People who wander away and then return do need relationships, just like you do. They need people who care about them. So if at all possible, be a friend to them and give them some of your time. That will be a wonderful gift they treasure
May God help us handle properly those who wander away...