The answer is that u are confusing two different concepts. Moshiach of the generation and THE moshiach are two different things. Not every moshiach of the generation lives forever. THE moshiach will live forever tho and based on everything there are those that say it applies to the Rebbe.
@Seichal HaYashar
Glad to see ur still going with the insults. I have to agree with u that hating me and calling me an am haaretz is going to bring moshiach. That was definitely clear from the sichos. U say we are representing chabad and I should essentially be a doogma chaiya, but u just get to insult people whenever u want right?
I plead ignorance as I wasn’t sure what the nature of the the source was (book, responsa, essays) Point being he wrote something to do with choshin mishpat which lists what will happen with moshiach. But thanks for pointing it out so nicely.