The absence of the king produces a cascade of structural consequences that transform the fanfiction system from feudalism into something else entirely.
1. The hierarchy becomes a flat oligarchy, not a pyramid.
Real feudalism is a pyramid. The king is at the apex. Below him are the great lords. Below them are the lesser lords. Below them are the knights. Below them are the serfs. Every level derives its authority from the level above it. The pyramid has a shape. It has a direction. It has an apex.
Fanfiction feudalism is a plateau. The Lords of the Ancient and Noble Houses are all at the same level. There is no one above them. There is no apex. There is no direction. There is no shape. The lords do not compete. They do not fight. They do not overthrow each other. They attend the same balls. They intermarry. They sit on the same Wizengamot. They form a club, not a battleground.
This is a gentlemen's agreement among petty despots, enforced by "Mother Magic," with no one above them and no one to check them.

2. Legitimacy becomes circular.
In real feudalism, the lord's authority derives from the king's grant. The king's authority derives from God, from conquest, from election, from ancient custom — but it has a source. It is grounded in something beyond itself.
In fanfiction feudalism, the lord's authority derives from... the blood. And the blood derives its authority from... "Mother Magic." And "Mother Magic" derives her authority from... being Magic. And Magic derives its authority from... being the fundamental force of the universe. And the fundamental force of the universe derives its authority from... being the fundamental force of the universe.
The legitimacy is circular. The system justifies itself. The blood is sacred because the blood is sacred. The oath is binding because the oath is binding. The hierarchy is eternal because the hierarchy is eternal. There is no external source of legitimacy. There is no king who grants the title. There is no God who ordains the order. There is no constitution that establishes the system. There is only the system. And the system says: "I am legitimate because I am the system."
This is tautology. And tautology is the enemy of politics, because politics is the art of contesting legitimacy, of arguing about who should rule and why.

3. Justice becomes impossible.
In real feudalism, the vassal who is wronged by his lord can appeal to the king. The king's court is the court of last resort. The king can hear the complaint, examine the evidence, and render judgment. The king can correct the system.
In fanfiction feudalism, there is no king. There is no court of last resort. There is no appeal. The lord is the ultimate authority within his own domain. If the lord wrongs his vassal, the vassal has no recourse. The blood oath binds the vassal to the lord. The magical contract enforces the obligation. "Mother Magic" sustains the system. And there is no one above the system who can hear the vassal's complaint and say: "This is unjust. I will correct it."
The vassal is trapped. Not by the lord's soldiers. Not by the castle walls. Not by the economic dependency. But by the ontology of the system. The vassal's very being is structured to prevent disobedience. The vassal cannot appeal because there is no one to appeal to. The vassal cannot resist because the resistance is magically impossible. The vassal cannot flee because the blood oath compels return. The vassal cannot even imagine freedom, because the imagination is bound.
This is not feudalism. Feudalism, for all its brutality, left gaps. The serf could run to the city. The vassal could appeal to the king. The lord could be overthrown. The system could be reformed. The gaps were the spaces of freedom — small, precarious, often closed, but real.

4. Reform becomes impossible.
In real feudalism, the king can reform the system. He can abolish serfdom. He can limit the lords' powers. He can grant charters of liberty. He can establish parliaments. He can create courts of justice. He can change the rules.
In fanfiction feudalism, there is no king. There is no one who can change the rules. The blood oaths are eternal. The Ancient and Noble Houses are permanent. The hierarchy is immutable. The house-elves are bound forever. The Muggle-borns are tolerated but never equal. The system is frozen in amber. And the amber is "Mother Magic." And "Mother Magic" does not reform. "Mother Magic" does not change. "Mother Magic" does not evolve. "Mother Magic" sustains. And the system is sustained. And the system does not change. And the system will never change. And the system is eternal. And the system is good. And the system is the order. And the order is "Mother Magic." And "Mother Magic" is the order. And there is nothing above the order. And there is nothing outside the order. And there is no appeal. And there is no reform. And there is no change. And there is no hope.

5. Unity becomes impossible.
In real feudalism, the king represents the unity of the realm. The king is the one who says: "We are one people, under one crown, subject to one law." The king is the symbol and the substance of national identity. Without the king, the realm fragments. The lords pursue their own interests. The regions develop their own customs. The jurisdictions overlap and conflict. The realm becomes a patchwork, not a unity.
In fanfiction feudalism, there is no king. There is no unity. The Wizarding World is a collection of competing houses, each with its own interests, its own obligations, its own private army of house-elves and bound vassals. There is no "Britain." There is no "the Wizarding World." There is only the House of Potter, the House of Malfoy, the House of Black, the House of Weasley, each pursuing its own interests, each enforcing its own blood oaths, each maintaining its own ancestral wards. The Wizengamot is not a parliament. It is a meeting of the club. The Ministry is not a government. It is a secretariat. The realm is not a polity. It is a portfolio.
And this is, perhaps, the most revealing consequence of the empty throne. Because the fanfiction writer does not want a polity. The fanfiction writer wants a collection of privileges. The fanfiction writer does not want to govern. The fanfiction writer wants to be governed by the glamour of governance. The fanfiction writer does not want the responsibility of unity. The fanfiction writer wants the aesthetic of unity — the ancient names, the ancestral manors, the Lord rings, the blood oaths — without the substance of unity — the common law, the common defense, the common good, the common king.