I’m afraid there’s not much help I can give you, with Activity Logs being disabled…
The only thing I can think of is if Google Analytics was installed (and tracking admin pages, which is rare) you might be able to see which IP triggered the deletion (you would have to analyze the query parameters, but all info is stored by Google).
Also worth asking: is there a chance the page is in the trash, still? Default trash holds for a couple of days, I think, and if they deleted a page and emptied the trash with it, that’s more than one screw up from the client, no?
Anyway, good luck! Sorry I can’t be of more help…
