A very good question

Can a person live off of world after salvation instead of Christ?

Answer: I think Paul deals with that specific subject

1Co 3:1 Brothers, I was not able to speak to you as spiritual people but as people of the flesh, as babies in Christ.
1Co 3:2 I fed you milk, not solid food, because you were not yet able to receive it. In fact, you are still not able,
1Co 3:3 because you are still fleshly. For since there is envy and strife among you, are you not fleshly and living like ordinary people?

Paul was addressing it to immature Christians IN the Church. So it would seem that once a person has actually made a commitment to Christ they then can run back to the world and live in the flesh. Now if they are a child of God and have the marks of a believer (Hunger for God, Hatred of sin, Heart for the lost, Growing in Holiness) then God will deal with them as dear children and discipline them (Heb 12:6-7).

The other thing we must do to understand the Word is to take all scripture into account when rendering a theological position.

1Jn 2:4 The one who says, "I have come to know Him," without keeping His commands, is a liar, and the truth is not in him.

It is clearly understood in scripture that there will be a lot of false converts (Mar 4 - The Parable of the Sower) but as a man we can only look onto the flesh and not the heart (1Sam 16:7). So it is never up to me or any pastor to tell someone they are saved...that is between them and God (2Cor 13:5)