Sechel…first you brought “sources,” in sdei chemed and abarbanel, which i answered.
Then you had no answer, so you pivoted to another “source,” a kasha…so to speak, on a rambam.
Then i “answered” it, as it were….then you go back to the 2 fake sources as proof that it’s not a chidush.
And around and around we go.
Techias hamaysim is a given, chazal say one who denies it is min hatorah is a kofer… and something the rambam writes extensively about. It’s not a chidush in that sense. And it’s no more of a neis than krias yam suf, which did not change the world forever; it was a one time thing. That’s why techiyas hameisim is not at all a stirah to olam kminhago noheg; the rambam is coming laafukei many midrashim about bread growing on trees, objects saying” today is shabbos” to a would-be violator, and other such examples of a new world order. The rambam holds that those medrashim are not literal. He holds that the world will be the same physically, but why does that mean that individual miracles won’t happen? Of course they could!
Remember, the rambam holds that techias hamaysim is a one-off for tzadikim to be able to see moshiach, something they hoped for all of their lives. Olam haba is not here, according to the rambam, it’s in shomayim. The ramban argues and holds that techias hamaysim is forever, in this world; people will live forever in this world, which will become olam haba. The ramban argues with the rambam on olam kminhago noheg too, and the achronim by and large follow the ramban, especially in light of the zohar and the mekubalim.
Could be that the Lubavitcher rebbe gor confused about the two opinions and asked a kasha on the rambam based on the assumption that techias hamaysim is forever, like the rambans shitah, because that indeed is a shinui. But those are two separate opinions.
In all of the seforim which discuss moshiach, there is no mention of him being from the dead, except for the abarbanel, who holds rhat techias hamaysim can happen first, and whoever moshiach is could very well be from those resurrected, but he does not say that it will be someone held of as moshiach who failed to accomplish his mission.
Again, the rambam disqualifies any candidate who does not fulfill his mission. So yes, it’s alecha lehavi raya, it is upon you to prove otherwise.
This is like someone saying that the avos wore shtreimels. Then someone asks, what’s your proof? The person answers… Do you have proof that they didn’t? Aha! You have no proof, so I’m right!