I think he is 30 years behind the times with that notion, lets say it was my Yeti and the diff breather was submerged, the sudden cooling of the casing sucking in a good quantity of water plus that which would come in through the static head, several months later I present the car under warranty with a knackered diff, Skoda would quite rightly refute the repair due to water ingress, even if they didn't they would not repair the differential, its a specialist job, the parts are not available through VAG, aside from the time and cost they could not guarantee the repair as they could a new unit, nope it will be a bill of 4.5k plus labour to the customer.
Hell the exact above has happened scores of times due to the incompetance of their own service technicians draining the diff instead of the Haldex unit yet that still does not get taken up by the media.
If they are not going to repair something that every garage in the 50's and early 60's were capable of they certainly are not going to be messing with a high voltage battery pack swimming in corrosion even if the parts were available and they had certified technicians, the battery pack will be sold on to one of the specialist reconditioners but dependant on how long it remains wet even they are unlikely to be able to salvage much other than the casing, even that is dubious as electrolytic corrosion will have been having a field day.
Anyone that says the battery pack should resist submersion is talking out of their backside, anything with service penetrations (cables, pipes, breathers, submarine propeller shafts) will leak to some degree, I designed military equipment which could be used outside in thunderstorm or resist a water cannon, far worse than a Tesla driving through a puddle (which of course was a porkie) but often the only way we could meet the submersion requirements (think falling off a raft during a river crossing etc) was to adapt specialised transit cases for the equipment made by other MOD suppliers.