How would you live your life if you truly were doomed to hellfire because of this sin? I don't want to hear anyone say that if you are worried about it, you haven't committed it. Please just give me a straight answer to this question please.
I perceive you are wisely seeking a phenomenological reply (how do they experience experience) and that is what I am endeavouring.
The people that you describe teach their followers (us) to feel that they are following a superior human leader (because they don't believe in distinct Holy Spirit actions). Some of them (we don't know which) are capable of turning round.
(Mostly, ordinary believers like us will need to ask God to help us find a church that isn't like that.)
(Some of them make a show of Holy Spirit beliefs. The scene is subject to fads and fashions.)
Not all the CF members answering here condone that atmosphere in the churches / preaching places that they frequent (for example I don't), but some do.
It took me a lifetime of figuring out (because it doesn't get explained) and wandering around religions and sects, myself.
As for the "doomed" part of your question we can only get as far as our guesswork as temporal beings allows. It would be something God would see coming (with sadness) because He having offered true belief through Jesus, Holy Spirit and the first apostles, is in eternal Present.
The particular piece of discernment we are asked to make is whether a preacher is good enough for us to be taught by, or if we need to look for better ones. Scriptures imply there will be some, so "doomed" is conditional. In regard to prominent christian spiritual leaders in danger, we should essentially pray they in general will turn round.
Those that are so deeply into their conviction that they don't need to turn round from promulgating these delusions, and their most craven hangers on, may turn out (one day) to be the doomed ones.
You've now got me thinking and praying, about which acquaintances (who are between preaching jobs) I could help with this problem, so thank you.