Since no battery technology is 100% failure proof, I would have to say that mitigating the potential issues of fire, or damage to other systems in the electronics bay is a big step to making a Li-on battery failure on a 787 a manageable event.
Hopefully, more information as to what exactly the failure mode with this individual cell was in this event, will lead to future improvements in the battery and charging system.
Now I have a question for those with more in depth knowledge of the 787 electrical system. My limited understanding suggests that if the main battery on a 787 were to become unusable, the APU battery can be switched to the 28Vdc bus, providing a backup to the 787's main battery. I'm also under the impression that the APU battery is only used to start the APU on the ground when no other power source is available, and that an APU start when at least one of the main engines is running is done with power from the main engine generators. Am I correct in this thinking?