That is interesting. I looked it up on wikipedia and the Argonaut / Paper Nautilus "shell" is a thin walled eggcase and that males do not have. It does not provide protection.
Female argonauts have the shell their whole life long, and do not only construct it when they have eggs to put in it. We may reasonably assume that it has survival value even when there are no eggs. We know, for example, that they carry bubbles in it to tune their buoyancy.