InfiniteFaith said:
What if they were unaware of their heresy as an adult? Or what if they did not meet the requirements of mortal sin?
Sorry to be so long in getting back to you, duties in the house.
We were discussing some of this with the visiting priest after Mass, today.
In answer to first question, if they are unaware of the heresy, their culpability is lessened. But just as in the case of invincible ignorance, where the sin won't be imputed to one, who didn't know of the Catholic Church, it is not a means of salvation, either. I really recommend reading Archbishop Hay's writings on all of this,
http://franciscan-archive.org/apologetica/extra.html. He covers everything and goes into great detail, using scriptures, explaining that God wants everyone to be saved and "requires of all men to be united to the Church by true Faith, as a condition of salvation, and, therefore, daily 'adds to the Church such as shall be saved,' "(Lk. ii.47) He goes into explanation of the two conditions why one may be outside the Church. Sin is one and I forget the other.
I also recommend Fr. Paul Trinchard's book "All About Salvation." Father used to tell us to quit playing God. Don't be a God of hate and don't be a liberal God.
Another good source is Fr. Michael Mueller writings. Also, Mgsr. Fenton.
Last but certainly not least, read the writings from the councils and the popes through the centuries. Can't go wrong with that!
http://traditioninaction.org/religious/n059rp_NoSalvation.htm