Thought - When Queen E is gone, does someone/something fill the void until they become their own sovereign countries (if they do?) Would President Trump/US possibly be the one to fill this position? I've seen bits and pieces pointing to this possibility. Would there be a separate position from US president to fill this position?

The Commonwealth realms:
Queen of Canada, Australia, New Zealand, Jamaica, Barbados, the Bahamas, Grenada, Papua New Guinea, the Solomon Islands, Tuvalu, Saint Lucia, Saint Vincent and the Grenadines, Antigua and Barbuda, Belize, Bermuda, and Saint Kitts and Nevis.