I agree with Jimmy on this. I can't convert anyone. I can influence people toward their own conversion but only God can covert. The heretic is deceived and actively working against the truth of God's Word by maligning it both to themselves and others. In most cases that I've observed, they are well-meaning people who were raised to believe lies and are held in bondage to those lies through fear. A very common theme in cults is that they are consistently taught that one loses their eternal salvation if they leave the cult and the cult's heresy. It's a very effective way to keep a person in bondage to heresy.
That said, there are people that are saved in my view that believe heresy. These, of course, are people who wrongly believe what we call non-essential heresies or heresies that don't impact one's salvation.