The plane would have imploded at depth. If the plane went into the ocean, there would have been a debris field regardless of how it entered the ocean.
The way you'd scuttle such a thing would be to land it on the water very carefully, in the style of Sullenberger or Kawasaki, get whatever you want off of it, and then flood it and let it sink. There would be no implosion because the pressure would be the same inside and out all the way down.
If it wasn't flooded, on purpose or not, it wouldn't sink. It would just be a very interesting piece of debris to find in satellite imagery.