Schism is a mortal sin, and whoever dies in that sin, it is the same as it is with any other mortal sin(s), they *will* go to hell forever. While they *might* have less culpability then some others, they, like us all, will be judged according to God's word, His teachings and His laws - all of which He left with His Church which is the only place to find truth and live according to it - which is why outside of that Church, there is no salvation. They certainly will not be saved according to their own idea of what they determine or think should be acceptable to God.
In another thread (*) I was taught that, in order for me to sin, I need to be aware/know, without negligence, that what I am doing is a sin.
Believing that Rome is without a Pope is schismatic if God/Truth determine that the Pope is legitimate. If the Pope is legitimate and, in good faith, after great studies, I come to believe that the Pope is not legitimate, then I am not aware of my schism, therefore, I am not in sin.
If the Pope and the Catholic Church are legitimate and, in good faith, after great studies, I come to believe that the Pope and the Catholic Church are not legitimate, then I am not aware of my schism, therefore, I am not in sin.
If that teaching regarding awareness and knowledge of sin is accurate, then, someone who believes, without negligence, that the Orthodox religion is the true faith, is not in sin.
(*) I asked if I would die in eternal sin if I followed a schismatic doctrine and participated in schismatic Mass, Eucharist, etc.
However, I question this logic because if ignorance of sin is an "alternative" road to salvation, then why send his only Son on earth to die to save us from our Sins? Let us all be ignorant Jews (or muslims, or Hindu, etc.) and be saved...