Objective sin (or material sin) is distinguished from actual sin (or formal sin). The former is objectively a sin. It is immoral under the immutable eternal moral law, by its conflict with the love of God and the love of neighbor as self. But the person who commits an objective sin may or may not know that the act is sinful.
The latter is known to be a sin by the person who chooses the act, and the act is chosen freely. Usually, an actual sin is also an objective sin. The only exception would be if the person mistakenly thinks that a moral act is immoral, and yet knowingly freely chooses the act; in such a case, the act is an actual sin, but not an objective sin.
Objective sins can be mortal or venial. Actual sins can be mortal or venial.
A mortal sin is so gravely disordered as to be incompatible with the state of grace, and the love of God and neighbor. An objective mortal sin is objectively gravely immoral. An actual mortal sin is a grave sin committed with full knowledge of its grave immorality and full deliberation (full freedom of choice).
Suppose that a person is committing a type of grave sin, on a continuing basis, without repentance. The sin is an objective mortal sin. But we cannot assume that the sin is also an actual mortal sin. We do not see the conscience of the individual. Thus, such a person might still be in a state of grace, if his objective mortal sin lacks the full culpability of an actual mortal sin. And as a result, the person might still go to Heaven, by way of Purgatory, despite not repenting from an objective mortal sin.
Therefore, it may be the case that persons who reject Catholicism, or who reject Christianity, or who reject belief in God entirely, or who commit objectively grave sins (contraception, sex outside of marriage, divorce and remarriage, homosexual sins, same sex marriage, etc.) without any outward sign of repentance, might still be in a state of grace, and therefore may still obtain eternal life in Heaven — probably after a long stay in Purgatory.
Please take a look at this list of my books and booklets, and see if any topic interests you.