Dranobob:

I grow apple trees. I have never had Cedar-apple rust in my 22 tree hobby orchard but I do spray for it. Not sure where you are located, but in my area I spray with myclobutanil in May to prevent cedar-apple rust. This is a fungicide commonly sold under the trade names Sprectracide Immunox, Eagle or Rally to name a few brands. While rust can reek havoc on the fruit and leaves it should not kill your trees.

I am not sure of a "systemic product" that is applied to the roots and taken up into the leaves except for imidacloprid which I would be afraid to use. I will assume that whatever your professional tree trimmers used was hopefully safe and legal for use on fruit trees. I only mention this because I am not aware of any such product, but not saying it does not exist.

The loss of all or most of the leaves by jap beetle can certainly weaken your tree. Japs can be controlled by spraying the tree with Sevin or another registered insecticide. Are your trees short enough that you can spray them to help save whatever leaves you have left at this time?

Even if the beetles strip the entire tree I would not think it would kill the tree unless it happened for several growing seasons. I have seen old crabapples totally defoliated by apple scab in August and yet look fine the following spring when they leaf out. My cherries sometimes get hit hard from cherry leaf spot. One was fully leafless also by August one year and was ok the next growing season.

I would still suggest trying to reduce the beetle levels and keep on as many leaves as possible for a healthy tree. Trees without leaves are not going to produce fruit.