If the crew have time, there is an emergency switch which alerts the ground station and increases the polling rate. If they land safely without having done so - or for other reasons - they can use the satphone function and, if neither apply, there need to be good overdue procedures in place. An example of poor flight following of a skytrac equipped aircraft is the 76 C++ accident in the GoM in 2009. I had to land 'in a hurry' a few years ago in a fairly remote area, and without the skytrac to a) communicate and b) give our position it would have taken a lot longer to retrieve us (thanks 7th Flight
)