Donate it to a college or high school sculpture class for a budding Michelangelo to work on.
Is it that distinctive plain headstone we see at Arlington and other cemeteries? Unless that style those used by non veterans too, I wouldn't think someone who wasn't in the service would re-engrave it (and if they were, I guess they would just get their own through the VA), but maybe.
Donating it to a school is a thought. There is one nearby that does have sculpture classes. If we can't use it DW might go for that.
It is just a granite slab, 2.5 feet wide, 1 foot tall, 5 inches thick, intended to be flush with the lawn at the cemetery.