I suspect only if God reveals themselves.
Will God still be invisible/immaterial? Without evidence I suspect some will still be skeptical.
The existence of Heaven would constitute a degree of evidence, as would the continuation of life in a different form post-death.
Sure, there are some atheists who believe in a form of afterlife despite a lack of belief in God. But in heaven? Few and far between. And confusing to me, but that's different story.