[FreedomStar3028]

Nor were any of the disciples dead at the transfiguration on the mountain/hill.

[DouglasKC]

Truly I say to you, there are some of those who are standing here who will not taste death until they see the Son of Man coming in His kingdom.“

They didn't have to be dead. He gave them a VISION of the kingdom of heaven. A glimpse of the future.

Matt 17:9..."Tell the VISION to no one until the Son of Man is risen from the dead".

The word that's translated "vision" is horama and it always refers to a supernatural vision in the new testament.