We have freewill to fall away (or not) as disciples of Christ. Yes, you can be saved and be a “lazy” Christian, (Although God doesn’t recommend this. You certainly won’t be winning many crowns in heaven.)
If we’re talking about a Christian that let’s say turned Atheist after going to college; the question becomes whether they truly accepted Christ in the first place (Only God can be the judge of that). If it was genuine, they’ll still go to heaven (Our works doesnt affect salvation once we’re sealed, good nor bad. You can think of it like an insurance policy for your soul)
Our salvation (of our Spirit/Soul), however, is FOREVER sealed by the Holy Spirit because of what Jesus Christ did on the cross for our past present and future sins (of our Body/Flesh). (Colossians 1:22-23, Colossians 5:8) This doesn’t mean we don’t believe in repentance, we certainly do (Romans 2:4-5), “There’s nothing I can do about my sin condition,” which leads us into Faith, not works (Ephesians 2:1-9), which then leads us into security of our eternal salvation (1 John 5:13).
Our WORKS (whether good or bad, it doesn’t matter) does *not affect salvation*. In your example, “rejecting Jesus” later in life is considered a WORK (albeit a bad one). So it still doesn’t matter. They are saved. Anyone that associates WORKS with Salvation is teaching a heresy.
You can be crying on your death bed “I DON’T WANT TO GO TO HEAVEN” Doesnt matter. Once saved you’re forever sealed by the Holy Spirit.
Btw, Predestination/Freewill has nothing to do with this conversation (Predestination is calvinist doctrine, which I don’t believe in, since I believe in free will).
If it comforts you thinking that we’ll have to prove ourselves through our works during the tribulation, being a hero and running away from the Anti-Christ from cutting our heads off, I won’t stop you. Either way, I’ll see you in the clouds
Episode VI: Awaken the Miracle 