What happen after the death of kings and queen?

Answer 1

If you are talking about the current queen of the UK, then I believe at her death there will be no queen, at least for a time. Charles, if he survives Elizabeth I, will instantly become king, but Camilla will not instantly become queen. Charles will become king because he is next in line to the throne and according to current law kingship is transferred at the instant of his predecessor's death. Even if at some future time Camilla is granted the title of queen, and that seems unlikely, she will never be reigning queen; she is not in line to the throne. She would be consort to the reigning monarch just as Prince Philip is consort to Elizabeth II. It is interesting that female consorts are sometimes styled as Queen, as was the mother of Elizabeth II, but I believe male consorts are never styled as King.

It could be that Catherine, William's wife, will be the next queen, and she will be queen as Elizabeth's mother was queen: queen consort and not queen regnant. If everything goes as would naturally be expected, with no one dying before his/her time, then the soon to be born child of William and Catherine, if a girl, will be the next queen regnant, the next reigning queen of the UK.

*As a side note, at the time of the Edward VIII crisis, Edward proposed, as an alternative to abdication, that a marriage to the already divorced Wallis Simpson could be designated as a morganatic marriage, meaning in part that Wallis and any offspring with her would be denied royal status and would be prevented from inheriting anything from Edward, including the throne. That proposal was not acceptable.

Answer 2

The widow of a king is called the Queen Dowager. The mother of Queen Elizabeth II, the widow of King George VI was called the Queen Mother until her recent death.