They would not be concerned about the electronics being damaged so much as recoverable so the components used can be analyzed and the supply chains traced. They want to know whether any export-restricted gear was used and, if so, who is to blame.
Jokes aside, I think the analysis will be more angled to proving or disproving the purpose, and identifying intelligence it gathered through some forensic analysis. If it dips into salty water, all circuit boards are immediately shorted. Seems a bit counter productive to me.
Of course things can still get shorted and damaged at the connectors, but the whole thing wouldn't be destroyed by water.