Regarding ur reading of the Rambam, i should point out a few things. 1. We learn from the Rebbe that the Rambam is very mediek(specific and careful with every word). It says killed not died. And u will notice every time he mentions someone who isn’t moshiach(bar kochba, yoshke, and the laws of a possible person u mentioned) is because they were killed. The part which u quoted afterwards which says he’s “like all the kosher and complete kings of Israel that DIED” can be understood as saying that even tho someone who was killed cannot be moshiach, he should be considered kosher and complete and his name shouldn’t be defamed just because he failed. Rather he’s even like the kings of Israel that didn’t fight wars and tried to be moshiach. Rather he is kosher and whole and even tho people died(since he lost and u might blame him for the deaths of Jews or resulting severe decrees) he is considered whole and kosher. This interpretation takes into account A. That he was wordy with “kosher” and “whole” and B. That he says he is like the kings of the house of David that died instead of a Loshon indicating previous contestants. C. “Killed” “died” and “not succeed”. Just say “if he didn’t succeed” and we would know that if he died or was killed that it was included. Instead he’s much too wordy. In addition, earlier the Rambam said “He and all the Sages of his generation considered him to be the Messianic king until he was killed because of sins. Once he was killed, they realized that he was not the Mashiach.” but he could have switched “Once he was killed..” with”Once he died”.
1B. Another way to look at it is al pi teva. Being killed was singled out by the sages as expressively not promised by the Torah, but there were opinions which held Daniel or David could come min hameism. Perhaps the Rambam considered it possible, but just not technically possible al pi teva. howevwr, if we merit, then we will receive miracles which bring the redeemer from the dead against nature. This interpretation is based on an opinion brought by the sdei chemed that with enough merit we will have moshiach min haneisim. This opinion also matches the format of the Gemara before hand where it considers what would happen if the Jews got the redemption through no merit or through a merit. Moshiach from the dead corresponding with the Jews doing teshuva, moshiach on clouds of heaven, achishena etc. even Berger in his book, while trying to demean the opinion, says that this is technically possible but he didn’t do enough reading. Additionally, the Rebbe says that Rambams laws are lo zachu and that if we merit then all the criteria could happen “bRega Echad”. He said we merited this and more. Anyone holding by such an opinion would blow the Rambam wide open. He could be in the resurrection, fight wars and win instantaneously. My point is not to spell out the Rebbes opinion(the Rebbe personally says we merited a higher level of bitah mixed with acheshina), but to show there are obvious ways of looking at this Rambam in a way that permit moshiach from the dead. It’s not as fridged as u might think. Another example is the son of the holy Ruzhiner who said that a few hundred years ago we would of had to wait 40 years til the redemption, but we merited that techiyas hameisim will happen the same time as moshiach so now his father, the Ruzhiner, can arise and be moshiach. There is also a source of a big chasid who said the Baal Shem tov will be moshiach.
2. First of all the Rebbe said he was ALREADY a navi based on many nevuahs which happened many times before. Things which are in printed in sichas clearly for anyone to see before they happened, and which were published in newspapers. There is a picture of the Rebbe taking an article with the title “yesh navi byisrael” with the Rebbes face on it to the ohel. If u want to challenge the Rebbe is a navi, it is against the Rebbe—not me. And if u think that calling the Rebbe a navi sheker ch’v ch’v G-d save us all by using as ur source a sentence in the Rambam which the Rebbe knew like his name, as well as all of Shas I have to wonder what on earth ur thinking. Before calling a holy gaon with ruach Hakodosh documented on thousands of videos and letters a navi sheker I consider u think over the dirtied up grain of knowledge u have of the Torah vs him. Really think about it. I want to be nice, but I’m not going to play a long with u if u insult such an amazing person. That’s pure hatred. I’ll try to hold myself back next time from showing any hints of disrespect. I want to address ur point, in as much as any of it was sincere. The nevuah of “henei zeh moshiach bo” was not in anyway a false nevuah because it was not saying that moshiach is redeeming everyone right now and ischalta degeulah arrived. There is, as found in many mefarshim, the idea that there is the coming of moshiach as a person and then the actual redemption. The nevuah which is based out of a midrash on shir hashirim means that moshiach the wrist is here and is telling the Jews to prepare for geulah because it’s coming for this generation. And as the mefarshim explain, the geulah with mirror geulah of mitzraim. We saw by moshe that he told pharaoh to let the Jews go and then things got WORSE. We also see that Satan said moshe passed away(in fact the mefarshim on Zohar such as the ohr hachama say that Moshe’s concealment on the mountain resulted in his leaving his body. In a way the Satan was telling the truth). The Rebbe also points out that a Helem v hester of moshiach does not contradict the Rambam so let’s just consider this it shall we. Many places say that the times right before moshiach will be really tough and people will struggle to believe in him. In fact the Rebbe Rashab did an open nevuah(as the Rebbe says) in saying that there will be a time when Jews will scorn the idea of moshiach. Sources say that there is a korach and gang in every generation causing problems for the nasi hador. Gedolim all around are saying moshiach is due any minute, but where is the big test? Who is turning the world over with yiddishkeit? The holy hidden tzaddik (zveil) was once told that the Previous Lubavitcher Rebbes comments about the messiah are uncomforting to him. The tzaddik responded “the secret of moshiach has been given to the Lubavitchers and it is permissible for them to speak about it”. Nobody else yearned and cried and made such a focus on moshiach, wouldn’t u think that that is moshiach? Additionally Rav Heller of crown heights paskened that the Halacha’s of chezkas moshiach are only if we have no other way of knowing, but if moshiach makes a nevuah—which then means we are obligated to listen— then if he says he’s moshiach then we are obligated to believe it. And a good nevuah never goes away.