Cherry Plum dying?
Does not look good. Cherries/plums are subject to a number of diseases. Read some of them here: https://library.ndsu.edu/ir/bitstream/handle/10365/17661/PP-689-1991.pdf?sequence=2
As well as a few insects. None of which can be diagnosed from this vantage point. Best recommendation is an onsite visit by a professional, namely a Certified Arborist, one who specializes in these matters. Find one or more Certified Arborists in your zip code at www.treesaregood.org Go to the Find an Arborist tab. Arborist evaluations are not expensive and where you can learn exactly what is going on in your tree. Good luck!