Would it be much worse than a car with a full tank of gas in the garage or a few cans of diesel for a generator? A lot more potential energy in those than this battery even if fully charged.
AFAIU, you can stop a gas fire by removing oxygen (e.g. with fire extinguishing foam or a lot of water). Lithium batteries burning reaction provides its own oxygen supply so you can literally do nothing to extinguish the fire. It can burn even underwater.