@741 It is against the realm of possibility that the Lubavitcher Rebbe will be Moshiach.
I am basing this in the fact that there’s never any discussion about a dead person being Moshiach before 1996. The Gemaras and ma’amoros that have been brought down are all re-interpretations by Chabadskers. Multiple Gedolim, and pretty much any Rebbi I ever asked has confirmed this, that it is not part of Yiddishkeit that Moshiach has already died.
There’s a famous story ( I don’t recall who it’s about). In the Alter Heim, a Rosh Yeshiva (or Rebbe) was on a train with his Talmidim/Chassidim and the bachurim were approached by a missionary. At first they humored him, answering all of his questions easily, but he finally stumped them by asking “Your Rabbis were mistaken about Bar Kochba, who’s to say they weren’t mistaken about Yoshke?” The Rov finally approached him and said “What made the Chachamim realize that Bar Kochba wasn’t Moshiach?” “Well, he died.” “Nu?”