[SeekAndFind]

If Ontology is the NATURE of ONE’s BEING OR EXISTENCE, are you saying that a person is BY NATURE, a Catholic because of Baptism and that he is by nature, a catholic until he dies regardless of what he believes in his heart?

[COBOL2Java]

If Ontology is the NATURE of ONE’s BEING OR EXISTENCE, are you saying that a person is BY NATURE, a Catholic because of Baptism and that he is by nature, a catholic until he dies regardless of what he believes in his heart?

"Until he dies" is irrelevant.

"Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation. Given once for all, Baptism cannot be repeated."
- Catechism of the Catholic Church, 1272

Death does not remove the mark from the soul.