Time
I'd suggest if there are no real developments in the next few days the international search assistance will reduce considerably. Most of the countries would have had time to get some updated aerial surveillance/intel of the area and contribute to the search effort. The fuel and resources are going to add up and with no new intel + the work done to date + satellite imagery, etc. there aren't good signs of it being found at the moment.
I'm sure digitalglobe could get some coverage there and use automated software/crowdsourcing to cover a bigger area over time.
As someone put earlier, the longer SAR goes on, the longer it takes to find something.