In a time of political upheaval, there are provisions in place for a staged transfer of power, designed with three goals in mind.
The first is the minimization of incentive for coup. There is no predetermined person or position within the government that is scheduled to take on the mantle of Regency during a time of crisis. Instead, a Regent is chosen by Parliamentary accord. This serves to avoid promoting a path of derelict ascendancy, and to discourage those who would scheme for such a turn of events. It is the assumption of our governing documents that such a legislative body will always have the wisdom to see through would-be usurpers.
The second is the assurance of stability for the commons during and after the transitional phase. During an interregnum while a Regent rules the land, there are categories of laws and decrees that cannot be altered without a majority vote from Parliament. Thus daily life for the people will not change dramatically when during the time of Regency, or shift drastically once a proper heir takes up the throne.
Third, and perhaps most important, is that a worthy successor is found. In order to rule out hasty action and to maximize stability, there will be no term limit or duration applied to the period of Regency. Historically, rash decisions have been greatly contested, resulting in extended political turmoil or outright conflict. When the proper heir is found and the position is filled by someone worthy of the role, all others will fall in and provide their support.