This has been a bad year for cherry trees and we have lost an ornamental cherry established for almost ten years, plus our older cherry tree is suffering badly. I also remember reading here of several people with dead trees.
If your tree still has green growth, it may not be that it is dying.
I would tend to do some formative pruning and now and reduce the branches just a little while the tree is still active to avoid silver leaf, and see what happens when it starts into growth next spring. If it continues to be ailing, then I'm afraid the best thing to do is to take it out and plant another one in a better spot with better soil preparation.

Bertiefox, Thanks very much for your response. Very useful