Well, to the OP.. this situation is really unlikely. A person who has been saved, given eternal life.. has the Holy Spirit dwelling in their soul, their spirit. This means.. when they do as you say.. and go wayward after having received eternal life.. they will be CONVICTED, and REBUKED for their behaviour.
Of course, they have free will to live as they will, but how would that go with the Holy Spirit continually convicting and rebuking them?
This is a possible situation though.. and a saved person who goes on to be ungodly, well they will miss out on rewards in heaven. But the place in heaven is set once they have been given ETERNAL life.
John 3:16, 5:24, Romans 10, 1 Peter 1:3-4, among many other verses are about this.
Jesus keeps someone saved.. by His indwelling. It's not the believers faith that keeps them saved.. because that goes up and down due to the human condition (sin).
But I will say, the situation the OP is speaking of.. is very unlikely.. given that at salvation.. the person is receiving Jesus Christ as their Saviour.. who then afterwards.. will teach, admonish, rebuke and empower this person.