With adequate resources the rest would be a matter of obtaining legal representation, but that's messy, expensive, and in this case completely avoidable.
What would benefit both parties here is an uncontested divorce, which means they both agree to all terms which mainly include property division, child custody, and support. If there's no property to be divided, and no support to be sought, then the only potential issue is child custody which it doesn't seem like Ralph cares about with Rosie.
Again, what Ralph wants is to be divorced from Pantsu as fast as possible. So if she offers him an uncontested, expedited, divorce then she can capitalize on this opportunity to be done with him entirely. On the other hand ignoring him or trying to negotiate for support (that he can't provide anyway) would draw out the issue to no ones benefit. Ralph might start pretending he cares about his daughter out of spite if he thinks they're trying to get in the way of him getting what he wants.