I don't think there is a way to tell the amount of left fuel, but technology could be implemented, all the data is centralized in the Flight Data Recorder. To send all this data via a satphone shouldn't be that much trouble. But hey! If this would have happened, they wouldn't have searched for MH370 for years :(
As far as pilots disobeying the Controllers, it sometimes happens and as the Air Traffic Controllers are the regulating authority they can fine the pilots or at least open an investigation which will trigger penalties from the airline against the pilot. Nobody wants a risk taker. A bad enough incident has the power to bankrupt a whole company. It has happened.
Thanks for the feedback!
It charges my batteries for writing more :p