Obviously it does exist. If in fact it was a seamount. Are there more? How many damaged subs are willing to risk? Who is to say if damage occurred again, the crew could make it back to a friendly port. The Chinese coaxed an AWACs out of sky, stole every bit of technology in it and returned the husk to us. Are we willing to give them a nuclear submarine?The US started really using subs in WWI. It was a small fleet, but effective.
In that 100 years, can you tell me how many time a US submarine has hit an underwater object that comprehensive mapping would have prevented?
It sounds like you have a great, albeit expensive, solution for a problem that does not really exist.
If we are not willing to seek solutions, we have no business being there and allowing it to happen again.