I leave the details to the Judge (Gen. 18:25), but if someone rejects and renounces Christ and is no different than their former state of godless unbelief, they are not a believer by definition (unbelieving believer is a contradiction in terms, oxymoron).
You divorce salvation from ongoing relationship and being in Christ, the condition for eternal life (since it is in Him alone, not apart from Him I Jn. 5:11-13 present, continuous tenses). You seem to reduce it to an irreversible metaphysical change parallel to physical birth. In reality, it is a reciprocal love relationship, not an unconditional zapping. Past sins can be dealt with, but this does not preclude the possibility of heinous future sins, including blasphemy, that cannot be swept under the carpet by a holy God (judgment starts with the house of God; Ananias and Sapp were struck down; I Cor. and I Jn. has temporal judgment of believer's sin by death).
Unbelief puts one outside of Christ and is the antithesis of saving faith, so the new reality of apostasy brings in new contingencies if persisted in.