There are treatments you can do to protect the trees, or ta least help protect them, but I don't know what they are...A quick Google search though...
This factsheet describes considerations and products for treating ash trees with insecticides to control Emerald Ash Borer.
hort.extension.wisc.edu
Next to me there is about a 5 acre wood lot and it is almost 100% Ash, and every one of them are dead. They are younger trees, probably 20-30 years old so not huge but tall. It looks like hell, and I suspect it will take a decade or more til they all fall and something else takes over.