I believe Moshe Rabbeinu's death is recorded several times within the Torah, but for instance here's the part recorded in Devarim:
And Moses, the servant of the Lord, died there, in the land of Moab, by the mouth of the Lord.
And He buried him in the valley, in the land of Moab, opposite Beth Pe'or. And no person knows the place of his burial, unto this day.
[Translation from Chabad.org]
The point is that no one knew where Moshe Rabbeinu was buried, even until this day. From the narrative, it seems that Hashem "hid" his grave. I have read and heard many interpretations as to why Hashem hid his grave, including that He didn't want Moshe's grave to become a shrine for avodah zarah, He didn't want the Bnei Yisrael to feel like they couldn't move on from where their leader was buried, etc.
But one thing really stands out to me. Devarim Rabbah 3:16 says that Moshe will accompany Eliyahu HaNavi in the end of days. This really struck out to me, because we know that Eliyahu went up to Shamayim alive, as recorded in Melachim II 2. If they are to come together, it would seem to make perfect sense that Moshe, like Eliyahu, did not die, but that he was taken up to Shamayim.
This would explain why his grave spot is unknown.
I suppose my question is, are there any sources that would support this claim? I am not specifically looking for sources from the Rishonim, but if they exist, then that would be best.