What is ultimately the fate of fontanels in a child or an adult skull?

The ultimate fate of fontanels in a child or an adult skull is that they ossify, and in time become sutures. Cranial sutures are fibrous joints between the bones of the face or vault. Once both fontanels and sutures fully ossify no further expansion of the brain case is possible. They are both important for brain and cranial vault growth. 

Yes all of them are right