The fear is not of apostates, most of can reason on our own. The fear is being found out; leading to loss of family, friends, and we do worry about the pain our leaving can give to still in ones.
There is also a fear of being 'poor" because of not planning better for something that wasn't ever coming.
The realization of death, not so much in itself, but the worry about the loved ones who may need us. And there is always something I want to do.
I did get a decent retirement if not extravagant, and always maintained life insurance for the family, wife in particular.