What happens in a Monarchy if the king dies and has no heir?

Answer 1

if the kiing or queen dies and has no hier to give it to then it goes to the next in line the eldest son.

Answer 2

If a king in a monarchy dies and has no heir, the line of succession becomes uncertain and may lead to a power struggle or a crisis of legitimacy. In some cases, a new monarch may be chosen through a process such as election, appointment, or selection from another noble family. In other cases, the country may transition to a different form of government, such as a republic or a constitutional monarchy.