We should separate the question “Does Salvation require belief in Mary’s Perpetual Virginity?” from the idea of rejecting the teaching of the Catholic Church. As it says on this page:
catholic.com/library/Salvation_Outside_the_Church.asp :
“while it is normatively necessary to be a Catholic to be saved (see CCC 846; Vatican II, Lumen Gentium 14), there are exceptions, and it is possible in some circumstances for people to be saved who have not been fully initiated into the Catholic Church (CCC 847).”
Therefore the Catholic Church allows that there may be circumstances in which salvation is possible without holding all of the beliefs of the Church, presumably including the perpetual viriginity of Mary. This is a different issue than consciously
rejecting the Church’s teachings however.