The first line of defense is a strong casing around the battery pack. Many lithium types need this anyway, due to charge/discharge issues. Like cars, the Empulse puts its pack inside the primary structure, which acts as a bumper. I'm going to take a wild guess here: the actual battery cells themselves may weigh less than the housing, since the housing also appears to include stiffener plates inside.
There is talk in the EV business of a "master cutoff" switch somewhere, for the sake of mechanics, emergency responders, and salvagers alike. Don't know where it would go or how it would look on an electric moto, but it would have to be someplace reasonably accessible and obvious, possibly standardized. Yet it would also have to be safe from vandalism. Thoughts?
Overall, however, I'm going to say that a box full of batteries is not significantly worse than the tank full of gasoline it replaces. In all debates over alternative fuels and their pros/cons, people forget that gasoline wasn't gatorade in the first place. In particular, an ullage space full of gas vapors is the definition of a bomb, which is why the military uses non-volatile fuels. In this case, I think the issue is more of first responders being too used to thinking in petro terms, and having to remember the quirks of, say, gaseous fuels as well as electrics. People would really rather just run with their assumptions, especially when put on the spot.