Moshe Did Not Die (although it looked that way)

...when Moshe Rabbeinu was approaching his death...he wrote 13 sifrei Torah...from the 'beis' of "Bereishis" to the 'lamed' of "b'einei kol Yisroel" and gave a sefer to each tribe and the 13th to the tribe of Levi.  Afterwards he ascended the mountain at midday on the 7th of Adar as our tradition specifies.  Then occurred that event which in our eyes they call death because we felt that he was missing and absent.  However, he has life in virtue of the level which he attained, and thus our Sages, peace be upon them, (Sotah 13) "Moshe Rabbeinu did not die" but rather he ascended and serves Above.  These matters, however, require very lengthy explanation and this is not their place.

Rambam, introduction to his Pirush HaMishnayos (Seder Zeroyim)