If you're going to use remote pilots to deal with anomalous conditions, you'd better have an emergency electrical supply that'll keep your remote control running for however long it'll take to glide at the plane's maximum range. You'll also need a communication system that'll work over the ocean, in poor weather conditions, while the plane is having difficulty maintaining a stable attitude (good luck maintaining the alignment of a satellite dish when the autopilot disconnects due to a sudden upset).
On the other hand, if your onboard autopilot is in control of everything, you run the risk of having autopilot bugs causing an accident - indeed, a software issue in the airbus flight protections (which, unlike the autopilot, are always active unless a very severe system failure occurs, and can override the pilot's inputs) has caused an incident that resulted in passenger injuries: http://en.wikipedia.org/wiki/Qantas_Flight_72
While none of this is impossible, it's certain to be expensive, heavy, have its fair share of bugs at the start, and by quite difficult to get past the regulators. Not to mention passengers probably won't be very happy being on an unmanned plane, even if the system really was perfect. So it's easier in the end to just put pilots on the plane.