In terms of leaving the sacramental and religious life of the Church, although one could never renounce his Catholicism due to the indelible mark of baptism, would one be in danger of eternal damnation for abandoning practice of the faith?
Yes, of course you would. If you stop practicing the Faith (i.e. stop hearing Mass, going to Confession, &c.), you are committing mortal sins which rid your soul of the sanctifying grace you received in Baptism and, should you die unrepentant, will condemn you to Hell. While Baptism does leave an indelible mark on your soul, that doesn’t mean you can’t forfeit the sanctifying grace you received in Baptism through sin.
How is anybody supposed to make a judgement about eternal damnation on such a vague post? Is the hypothetical person in this post renouncing Catholicism or not? Or are they just not going to mass anymore because they have, for example, clinical depression?
Jn 14:15 “If you love me, you will keep my commandments"