I did not watch the video...in case that explained something.

Based on the short description and the pic. I'm not sure how "mechanical failure and gale force winds" relate. Also based on the picture the ship is sinking in the stern, which typically means the engine room was taking on water. If an intake hose was knocked loose/came loose it would be dumping the intake water in the engine room, this issue could go unnoticed for just long enough to create a massive issue. The same thing happened to one of the fishing boats we use several times a year and considering it was much smaller they identified the issue quick enough.

Again this is just speculation as I'm not an expert of the mechanical workings of that particular yacht.

The only other "mechanical" failure that I would associate with an engine room flooding is the drive shaft dislodging but that seems highly unlikely.

 

So once a boat like this sinks do they just count it as a loss and leave it at the bottom of the ocean? Just curious, as I'm sure the raw materials alone are worth a few million dollars

 

Yep, not worth salvaging. There would be ( shouldn't be as it won't be insured in open water ) nothing of value on board. Boat itself is insured however.

 

Here's an interesting article about the sinking. They are obviously still investigating it, but the owner of the yard has spoken about the sinking.

Head of Proteksan Turquoise comments on sinking of superyacht Yogi

 

Wow!!! That is pretty crazy!! I would hate to have to evacuate in a situation like that!!