If Quran was not protected, it would be wrong to end Prophethood. But if Quran is protected, and God sends a succession of Messengers, and will send a Messenger to revive the revelation of Mohammad at the end times (the Mahdi will return), then is not cutting of God's hand.
In fact, there is wisdom, for the interpretation to win. In the past, the interpretation of the holy books was first to fall even during Prophets who would succeed the founding Prophet, people followed misinterpretations and eventually changed God's words. People despite clear proofs, mixed clergy leadership with that of God's chosen.
The holy books, The Torah, Gospels, most of it is about manifesting the position of God's guide on earth. There is still a guide that one day God will manifest through miracles in a way never the proof is never manifested to that degree "say: wait, we too are waiting".
Despite that, people equate leadership of non-chosen with chosen. So God decided to write Quran in a way, that guarantees it's protection. So he gave ways to misinterpret his words despite enough clarity, that he wishes to rebel against his chosen Messengers after the Seal of Prophets (the Successors of Mohammad starting from Ali), may rebel against them. Ghadeer even the words were calculated there to say in a way that allows for people to pretend to not know what it means, despite, the Wilayah there is in context of the Two Heavy precious objects, Quran and his family, and the Wilayah of Mohammad is in this flow, and it's clear it means whatever Wilayah Mohammad has over you, so does Ali.
The fact Quran was guaranteed protection meant it can't be as explicit, because if was manifestly explicit in Wilayah of Ali, then, either God would have intervene in this world in ways he doesn't like to protect the Quran or let it be distorted. He decided then to make it clear enough, but, only if you want to remember, you want to understand, you want to recite per God's interpretation.
In all that, he allowed Satanic forces to split Quran to parts, but then through Ahlulbayt (as) insights, unites the parts and they begin to hold and interpret each other and manifest the wonderous words of God.
The battle for interpretation is not over. This is God's plan.
So I don't see with return of the Mahdi, that God's hand is cut off. One can say, Bahaism with no present guide on earth and over 1000 years of not allowing God to send a Prophet, has put a temporary cut off his hand.
Anyone can play this game. Yes, it's a huge trial that God is talking to us through revelation after Mohammad and there is no current communication nor any communication from God to humans after Mohammad, but this is because Quran is comprehensive, and is meant for all times.