Unfortunately many passages are relevant to a topic like salvation. So taking one in isolation can be misleading. Jesus is asked specifically what is needed to be saved. He gives two different answers. One time it's the 10 commandments. Another it is love God and your neighbor. Those answers are related, because love for God and neighbor summarizes the law. Jesus is also big on God forgiving us. So it's likely a mistake to suggest that one instance of failing to forgive damns you. Forgiveness is, however, part of loving God and neighbor, so I think it's right to consider it part of salvation.
But how do you deal with the fact that for Paul, and I think also John, following Jesus is a matter of faith. What do we say about people who have faith in Christ but don't forgive people? Or people who forgive, love God and neighbor, but don't have faith in Christ?
I don't think these questions are so easy to answer. I have my own answers, but they're not the result of simply taking one passage and reading it straightforwardly.