Hi pilgrim,
I guess the simple answer is that all the things it says will happen in Mat 16:27-28 did not happen at the account of the transfiguration. But there is a historical case that (concerning the Matthew 27-28 verse imagery) can be made in regards to the siege of Jerusalem and the destroying of the temple around 70AD. And the simplest of all answers is that Christ was going (in regard to the transfiguration), not coming back. A voice came down from heaven, but the Christ did not.
Once again, matter of perspective. I tend to view it this way.
Thanks,
Chad