Anyone who is validly baptized (remission of Original Sin), and is free from mortal sin (only mortal sin can merit hell), is saved.
I have no idea what #2 was necessary in the Baltimore Catechism's answer, unless it was a poor way of saying that a baptized person (fully initiated into the Roman Catholic Church by virtue of their Baptism), who then knowingly and willfully separated themselves from the Faithful, could not be saved, as such an action would indeed comprise a mortal sin.
That all who die validly baptized and free from mortal sin will take their place among the Blessed is as certain a fact as anyone can ever possess.
Those separated from the Church are not free from mortal sin however. They are stained with the guilt of heresy, schism or apostasy.
In order for schism, or heresy, or apostasy, to be grievous sins which separate one from the Church, they must be formal.
Any Christian, at any given moment, is probably guilty of some material heresy, however obscure. But the good Christian, who has the fruits and gifts of the Holy Spirit, recants when corrected.
Others refuse to recant.
These fall into two categories:
1). Protestants, and,
2). Sedevacantists.
The Protestant refuses to recant because he thinks in his pride that he understands Scripture so well that no one can tell him different.
The Sedevacantist refuses to recant because he thinks in his pride that he understands the teachings of the Church so well that no one can tell him different.
But the good Christian wages war against his pride and humbles himself before those prelates whom God has appointed to rule over him.