How likely is it that they actually have survaced but nobody found them yet? Would sonar pick them up if their engines are out? How likely is a visual contact on the ocean if the sub drifted a few miles?
If they are on the surface, getting them by sonar is not possible, but aerial surveillance might find them. However, things are very hard to see in the ocean if there are waves. They might have an AIS locator which would transmit their position and an emergency signal, but maybe they skimped on that too, because the submarine-rated ones are expensive.