If you have time, cut affected leaves, but I doubt any chemicals will get through to the rest of the plant at this time...the leaf is probably dead and not moving anything through it. No matter how I cover plants, DH manages to make a mess of them when he sprays anything, and I've never had any longterm damage.
As for approaching your neighbor, just in a friendly manner ask to be notified in the future so that you can cover your plants that might get spray on them. In your neighbor's defense, it is amazing how far spray travels...until you've seen it, it's not possible to believe.

^I am not angry at them because they are nice people and I know they didn't do it on purpose. I just wish they had given me a chance to cover them. I didn't think it could have done this much damage either, but it did. I am just going to tell them that it did damage and to please let me know the next time they do it so I can cover the plants. I do think that with fall fast approaching, these leaves are going to be on the ground soon enough anyway. Surprisingly, my evergreen Rhododendron has yet to show any signs of damage...tougher leaves, perhaps?

being oct and all.. arent they all close to going dormant in your zone ???

i would just leave it all ... for fear of triggering a late flush.. which would be worse than some simple leaf damage ...

in a month.. or at fall cleanup.. get rid of the leaves ...

ken