This is the kind of discussion that is not useful. Jesus’ admonishment to Peter about not worrying about what happens to John applies to this subject. It only matters that Jesus died for my sins, and that He has covered my inequity with His righteousness. Jesus told us and Peter, Paul and John reiterated that this salvation is available to anyone who believes in Jesus and follows his commandments.
Jesus also told us that the road to Perdition was wide and the path to salvation was narrow. This is the Gospel that needs to be preached. It is a Gospel of individual salvation and not a gospel of collective anything.
This argument is engaged by those who believe that cultural Christianity and/or membership in a designated church makes one eligible for atonement.