Two-word term that arises after the death of a powerful leader?

The two word term would be Power vacuum.

Explanation:

A power vacuum is what happens when there is sudden loss of authority in the governance and there is no potent replacement of it in sight.

This is usually what happens after the death of a long reigning dictator or a strong leader who had held the country so that there was no other alternative ready.

So the stability of their governance leads no potent alternative and makes a power vacuum in the nation.

The power vacuum will be the void of no strong leadership here.