From the beginning of beta, the rule was always that if your sov dies it's game over. It sounds reasonable but after playing the game a bit I think that allowing succession is a natural, easy way to solve a few problems. For one thing, the sovs offspring tend to be even more powerful than the original sovereign. They could fill their shoes quite nicely I would think. The soveregns are suppose to be immortal according to the fiction, but let's face it, once the game starts it's a miracle to see them reach age 30! Yes, they die with alarming frequency. This is good and natural as long the kingdoms future is secured with an heir or three.
The game has evolved to a place where the sovereign's role need not to be so emphasized. All the pieces are nearly in place, might as well use em.