That's funny. No. They can put their support behind another contender than Mr. Y (and English history has it's share of examples of crisis of succession, btw).

That's funny. No. They can put their support behind another contender than Mr. Y (and English history has it's share of examples of crisis of succession, btw). In that case different factions that actually hold power get to duke it out to see whose candidate gets to be the new monarch/overlord/cesar/president. That is typically not peaceful, certainly not at the political level (think Tower of London) and may even involve actual guns and civil wars.