That was an interesting thought that Lark had just proposed very casually, prompting Tony to ask, "Is that...beyond the limits of a world? Death?" That was probably a question of faith, ultimately, which Lark clearly had in abundance, and other like-minded people would have different answers of varying specificity; Thor would agree that in death, people went to a different plane of existence, and it depended on the manner of death which one exactly. Tony didn't have that kind of conviction himself.