Basically there is a sicha, shmos likutei sichos chelek vov.
The Rebbe asks how is Moshe rabbeinu alive? After all, every tzadik is Af bimisosom kruyim chayim, so whats the addition of Moshe Lo mes?
The Rebbe answers that there is a medrash about Moshe, “Hu goel rishon, hu goel acharon.” Even though the Yiddin of the time didn’t merit moshiach, so Moshe wasnt moshiach, but the words of Hahem still were fulfilled.
How?
Moshes neshama is always present on earth in the body of the ispashtusa dMoshe bechol Dara. And since the main life of a tzadik is his Ruchnius accomplishments, Moshe Lo mes, because his neshama is always alive in the body of the Nossi hador,and that’s how hu goel rishon hu goel acharon because his neshama will end up with the Nossi hador who will be moshiach