I am inclined to say that this Cherry is way too gone. If you remove all the under weeping limbs and any dead limb wood, this tree will probably revert back to its original graft host. Sometimes, during stress situations and insect attacks, the tree will throw on top growth and eliminate the lower stressed limbs. It definitely appears to be in poor light, crowding, and poor air circulation........let alone neglect from improper pruning and growing site. I see weeping mulberries all the time that is allowed to become overgrown and the lower limbs will fizzle out from lack of sunlight. The top continues to grow out of the weep below the grafts. It isn't a pretty sight then after this happens it has no other choice but to undergo a reversion. You can treat this tree with neem.........I hope you have a good sprayer that can easily be cleaned afterwards. Neem isn't my favorite!! It is a oily--gooey mess afterwards to clean out of the sprayer. I use Chlorthalonil on these trees.........followed by a shot of Spinosad or safer's soap.