Tyranny is often destroyed from the outside by a superior regime. It is also destroyed from within when the rulers fall into factional conflict. Kingship is rarely destroyed from outside. Kingships are preserved by limiting the king's authority. Tyrannies are preserved by eliminating all potential rivals to power.
Extreme democracy is basically the same as tyranny.
A tyrant above all needs military virtue, and should command awe but not fear. He should be moderate in his dealings with women and strong drink, and he should show himself to be attentive to the gods. He should honor the good citizens personally and make other officials punish the offenders. The tyrant should not give preferential treatment either to the poor or the well-off. If a tyrant does these things his rule will be long-lasting and not completely vicious.