Oil slick depends on if there's any fuel left, and while initially there is a lot floating debris it sinks or gets spread over the ocean over the course of a few days.
The suggested area was searched first, if there had been floating debris it would have been found.
I think it's time to move on anyway.
I believe it would be possible to register a large sinking object hitting the seabed on a seismometer but the evidence suggests that the plane flew west over malaysia, so it's irrelevant.