1. Everyone who dies in the state of grace goes to Heaven, either directly or by way of Purgatory. This is already the infallible teaching of the Church. The criterion for who is saved is nothing other than dying in the state of grace.
Some say that perhaps the Blessed Virgin Mary did not die, but was assumed directly to Heaven at the end of her life on earth. However, it is already the ordinary non-infallible teaching of the Church that Mary died and rose, prior to being assumed into Heaven. Her assumption is an infallible teaching. Her death and resurrection is a non-infallible teaching.
It is possible for someone to be judged by God at the end of their life on earth without first dying. This may be the case for persons, in the distant future, who are alive at the time of the general Resurrection. Perhaps they do not immediately die and rise, but are given the particular judgment and then the general Judgment and the benefits of the general Resurrection, without having to die.
However, in the present economy of salvation, the only path to Heaven is to die in the state of grace.
“Above all, the state of grace is absolutely necessary at the moment of death; without it, salvation and supernatural happiness — the beatific vision of God — are impossible.” Pope Pius XII
2. There are three ways for someone conceived in original sin to enter the state of grace: (a) formal baptism with water, (b) a baptism of desire, or (c) a baptism of blood.
The baptism of desire can be implicit. “An act of love is sufficient for the adult to obtain sanctifying grace and to supply the lack of baptism.” Pope Pius XII
All human persons who truly love their neighbor are necessarily in the state of grace. Actual mortal sin is incompatible with the state of grace, and no one is able to truly love their neighbor without the state of grace.
So if an atheist loves his neighbor, then he is in the state of grace, despite not believing in God. His objective mortal sin of not believing in God must not be also an actual mortal sin, since he loves his neighbor. And the same is true for believers in non-Christian religions, for Jews, Muslims, Buddhists, Hindus, and believers in other religions, as well as atheists or agnostics. If you love your neighbor, you are on the path to Heaven.
Persons who are LGBT (lesbian, gay, bisexual, or transgender) go to Heaven if they love their neighbor. Persons who are in a same-sex relationship or same-sex marriage go to Heaven if they love their neighbor.
Someone who is guilty of objective mortal sin might not also be guilty of actual mortal sin, due to invincible ignorance. Each person is judged by their own conscience. And if anyone is guilty of any actual mortal sin, of any kind, they can repent by implicit perfect contrition. By an act of love of neighbor, they return to the state of grace, since love of neighbor implies contrition for all grave sins.
3. All prenatals, infants, and young children, who unfortunately die at that young age, go to Heaven. They die in the state of grace due to a baptism of blood, just as the Holy Innocents did.
The only persons who die in a state of “original sin alone” are adults who are guilty of the actual mortal sin of omission of never having found sanctifying grace in this life, despite ample opportunity. Children did not have ample opportunity, so they are given the state of grace prior to death — in the last moment of life prior to death, or at some earlier point.
4. Some human souls are sent to Hell by God, because they died unrepentant from actual mortal sin.
The universalist position, which claims that all human souls eventually go to Heaven is heresy. The mitigated universalist position, which claims that we may “reasonably hope” that “perhaps” all human persons go to Heaven is still heretical, since it is a hope that the heretical claims of the universalists are true.
5. But every human person has ample opportunity to find and obtain salvation.
“The universality of salvation means that it is granted not only to those who explicitly believe in Christ and have entered the Church. Since salvation is offered to all, it must be made concretely available to all.” Pope Saint John Paul II, Redemptoris Missio 10.
Many souls are lost to the fires of Hell, unfortunately. But the vast majority of human persons go to Heaven, most by way of Purgatory.
More in my book: Forgiveness and Salvation for Everyone
Please take a look at this list of my books and booklets, and see if any topic interests you.