Perhaps the discussion should be phrased instead as
how likely can a hypothetical operation as sketched by Mr Hersh, involving so many people in so many governments, remain without hard evidence leaking out for years?
Personally, I wonder what would have happened to the sonar buoy that was alledged to have triggered the explosives. Wouldn't they have to come back and pick it up to avoid leaving evidence of the triggering mechanism? And if they have to come pick it up anyway, why drop a buoy at all? Why not use that presence to send a time delayed trigger?