Can Non-Trinitarians Be Saved?

Questions about whether the heresy of modalism prevents salvation and whether the greetings in the apostles’ letters that don’t reference the Holy Spirit are evidence the early church didn’t teach the Holy Spirit is a person.

• Is modalism a heresy that prevents followers from being saved, and if so, what is it about it that is spiritually fatal to salvation, and what about those who don’t know it’s a heresy?
• Do the greetings in the apostles’ letters that don’t include references to the Holy Spirit count against the idea that the early church taught the Holy Spirit is a person?