Hi Audio Prophecy,
Yes and no.
It is an official teaching that "Outside the Church there is no salvation". But you also have to understand it in the sense it was written in. As the Catechism of the Catholic Church explains:
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"Outside the Church there is no salvation"
846 How are we to understand this affirmation, often repeated by the Church Fathers? Re-formulated positively, it means that all salvation comes from Christ the Head through the Church which is his Body:
Basing itself on Scripture and Tradition, the Council teaches that the Church, a pilgrim now on earth, is necessary for salvation; the one Christ is the mediator and the way of salvation; he is present to us in his body which is the Church. He himself explicitly asserted the necessity of faith and Baptism as through a door. Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, whould refuse either to enter it or to remain in it."
847 This affirmation is not aimed at those who through no fault of their own, do not know Christ and his Church:
Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and moved by grace, try in their actions to do his will as they know it through the dictates of their conscience, those too may achieve eternal salvation
848 "Although in ways known to himself God can lead those who, through no fault of their own, are ignorant of the Gospel, to that faith without which it is impossible to please him, the Church still has the obligation and also the sacred right to evangelize all men."
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In other words,
objectively speaking, it is a grave sin to not be Catholic. Makes sense, doesn't it? Since the Catholic Church
does claim to be true Church founded by Christ, then rejecting the Catholic Church is the same as rejecting Christ (cf. Lk 10:16).
But, as with any mortal sin, damning a person to hell if they die unrepentant, three conditions are necessary for it to be mortal:
"Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent". (cf. CCC # 1857)
For all non-Catholics, obviously the first condition of grave matter is met. But what about it being "committed with full knowledge"? How many non-Catholics actually
know that they are rejecting the church started by Christ? Not many. For those who do, then, of course, they would be committing mortal sin. But most don't and its not their fault. They believe that they are rejecting a church, which, even if they grant Catholics to be Christians (as many do thankfully), they still feel it contains some false teachings, and is not the true Church. That means they wouldn't be excluded from heaven on that basis alone. (Of course, they might be excluded from heaven on committing another mortal sin and dying unrepentant, just as a Catholic would. But not merely for being non-Catholic.).
Anyway, I believe that there are plenty of non-Catholics in heaven.
Well, I hope that my answer helps a little