I have read from a number of different people, that John was over 90 years old when he was on Patmos.

Yet he was told:

Revelation 10:11 And he said unto me, Thou must prophesy again before many peoples, and nations, and tongues, and kings.

After John left Patmos, did he already prophecy before many nations and kings?

If so, which were those kings?

Or could it be possible that John, himself, might be one of the two witnesses during the tribulation?

It did say, "prophecy again", so is that referring to something in the future end times?

Can that ever be true for someone who has already died?

Moses died and was buried at the end of Deuteronomy,

yet there he was on the mount where Jesus transfigured,

and Peter wanted to make him a tabernacle,

but that would not have been necessary if it was only the spirit of Moses,

so wasn't Moses there in a body?

So, could something similar happen to John?