Answer: If the deer are munching the buds off your tree, you'll be able to tell -- the branch tips will show the rough cut made by their incisors. If they're very hungry, I guess they may have eaten all the viable buds from the tree, which would explain it not sending out any growth from the top. Mountain ash is not very tolerant of wind or poor drainage. It may have suffered too much drying during the winter when winds are persistent. The tree is also succeptible to borers, so check the trunk for holes.
You can try to train one of the sprouts to replace the tree, and transplant it to a more sheltered site. Full sun is recommended. Best of luck!
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