These are my headcannons

The Status Ceremony

This ceremony is when the status of the country is passed to another entity, whether it is an insurgent, militant, special, or future country. Full-time entities cannot gain the status of country.

In order for a country/insurgent/special/ militant to be the head of a country, the country that is about to lose their status says:

I, [insert name], give up my status as the head of this nation and its people and bestow it to [country/insurgent/special/ militant's name].

Only then would the entity become a country.

But...

If they kill the country before they says this, the status of being the head of the country becomes a free for all. This might benefit the entity if they are the only person who knows that they are dead, as the country doesn't have to willingly give up their status. So they say:

I, [insert entity's name], take the status of the head of the people and nation from [dead country's name].

Without the fear that someone else would take it.

However, if a lot of entities know that the country is dead, they could say this, then it would go to the person who completely said it first.

This route of taking the status from a dead country is not often taken as the new country would have severe personalities shifts, and might even become incompetent in leading for a while because of this. This is temporary.