Shortly after the search switched to the Indian Ocean it was stated that it would take around 3 months for debris to wash onto the WA coastline, however the search was further away than now, so possibly only 8 to 10 weeks, at that time. Regardless, you'd think that something would have been sighted floating by now by one of the search aircraft.
In relation to MH370 remaining intact after ditching into the ocean it has been stated in media reports that there would only be a remote chance that it could have done so, however if you read through the link below you will see that this is quite possible and that even when sections of the aircraft have broken off that it can continue to float long enough for passengers to escape, before the inevitable sinking. If of course, as may have been the case with MH370, the passengers were already dead, then they would all have gone down with the plane.
There is a list of plane's ditching into water and the outcomes at the link below. It is surprising to see how many people have survived such ditchings.
As MH370 is believed to have ended up in the Indian Ocean, the following may be of interest:
"On 23 November 1996, Ethiopian Airlines Flight 961 (a Boeing 767-260ER), ditched in the Indian Ocean near Comoros after being hijacked and running out of fuel, killing 125 of the 175 passengers and crew on board. Unable to operate flaps, it impacted at high speed, dragging its left wingtip before tumbling and breaking into three pieces. The panicking hijackers were fighting the pilots for the control of the plane at the time of the impact, which caused the plane to roll just before hitting the water, and the subsequent wingtip hitting the water and breakup are a result of this struggle in the cockpit. Some passengers were killed on impact or trapped in the cabin when they inflated their life vests before exiting. Most of the survivors were found hanging onto a section of the fuselage that remained floating."
