The most significant threat to the stability of military dictatorships generally comes from inside the military. Consider the history of military rule in Guinea, a West African country. In April 1984, a military junta known as the Military Committee of National Recovery (CMRN) was established in Guinea following a coup led by Lieutenant-Colonel Lansana Conté. The coup took place after Guinea's first president, Sékou Touré, was assassinated.
As a result, when a dictator is deposed, he is likely to be replaced by a defecting member of his own support coalition. As a result, dictators should be replaced with dictators of a similar sort on a regular basis. Indeed, there is convincing evidence that this is the case. For example, Gandhi and Przeworski (2007) look at 388 authoritarian leaders who came to office after 1945 and departed power before 1996 for causes other than natural death.