Maybe look for a replacement case back and keep that one as a memento?
This sounds like a good solution. I had a watch with the original owner's name and ss# engraved on the back. I left it because it was perfect ID if the watch ever got stolen.
I don't know if the OP has any kids, but I would leave the engraving, as it would be a pretty awesome (and way more personal) thing to hand down in the future.
Alternatively, you could buy a new or used case back. Swiss Limited Editions has one for £499; https://www.swisslimitededitions.co...ster-hippocampus-case-back-moon-watch-1963-69