I think the only thing that will get rid of the monarchy is the Tory party.
Just as they are the party of "the Union", they purport to be the party of the monarchy.
They are the most likely to break up the Union, or at least see a united Ireland.
And they are the most likely to break the monarchy or at least reduce it if they can find a way to take the land, money and assets for themselves and "interested parties", rather than return them to the people, or do good for the people.