They can just give up. The search has cost well into the billions of dollars. after three years I guess everyone on the investigation team (while still searching for the plane) just pretty much said we are not finding anything and it is too expensive to keep the search going so lets end it.
Although I personally believe that they should keep searching, It is really expensive and is basically making the countries involved lose lots of money that could be used in health to save 100-1,000,000 people or many other places. But yes I think that the search should continue. (How about some other rich country take over the search in order to make sure that it never happens again).
Ps time has really flown (I think the ATSB report might be closed now as unknown or discontinued)
Edit I found the ATSB apparently it is going to Be closed in two months