“No, that’s not possible. The Rambam clearly says if he failed, it’s known that he’s not moshiach.
He failed. He’s not moshiach.”
DY
The Rambam is speaking abut the status of chezkas Moshiach. Without debating the diyukim that can be made about neherag, it is clear that contextually the Rambam is explaining that the status of chezkas moshiach ends when the melech is neherag.
But this certainly does not preclude the possibility of anyone anyways being Moshiach. In fact, the status of chezkas moshiach not even need occur. Perhaps all of the conduct of Moshiach will happen miraculously at once and there will only be Moshiach vadai.
There does not seem to be any halachic source which procludes Moshiach being a resurrected person and the Rambam in hilchos melachim does not prove such.