[ealgeone]

1272 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,

If this is the case, then mortal sins cannot cause one to lose their salvation.

[Petrosius]

If this is the case, then mortal sins cannot cause one to lose their salvation.

You left off: "… even if sin prevents Baptism from bearing the fruits of salvation."

[ebb tide]

If this is the case, then mortal sins cannot cause one to lose their salvation.

That is correct. If mortal sins are sacramentally confessed, with a firm resolution to sin no more, and absolution is given, there is still a chance of salvation.

St Paul participated in the murder of the martyr St. Stephen, but Paul himself is now a saint.