Most likely Pseudomonas syringae (lilac blight).

Been a lot of it going around this season from reports I've heard.

Supposedly the wet weather has caused the spread.

S. reticulata has some resistance but is still somewhat susceptible.

https://www.purdue.edu/fnr/extension/pseudomonas-syringae-pv-syringae:

Bill, thank you for the link. It does seem my tree has lilac blight. There was an incident last summer when the tree was unusually heavy with flowers and we experienced a torrential rain that collapsed the canopy. I pruned off some of the flowers to lessen the weight, which was probably a bad idea. As you mentioned, this year has been unusually wet, which most likely hasn’t helped the situation. I’m not sure where to go from here, but if it continues, removal might be required.

I have a 250 ft. hedge of Syringa vulgaris that look like they came direct from Chernobyl gardens.

And how would you perform the recommended method of restoring them by collecting all the dead leaves, burning them and cutting off all the affected branches too. :^?

My back just isn't up to that anymore.

I wouldn't mind removing them, but I can guess we're talking $$$.