The scary thing about a class D fire is that it is self oxidizing. They are very hard/impossible to put out. Usually the best you can do is isolate it from anything else that can burn and let it burn itself out, if you have the space and equipment and correct environment you can try and break it up, but that is a lot of ifs. Water can be problematic because there is a good chance it will just scatter a bunch flaming goo everywhere not put anything out. Usually the best thing to do is to stick it in a bucket of sand. Second best is to dump sand on it. Clay type kitty litter would be a good substitute for sand, it won't catch on fire, lighter than sand, it will absorb any molten residue from the fire.

My guess on the plane scenario, there are enough secondary effects (smoke, insulation/trim/carpet/seats catching on fire) that would bring down the plane. but I don't think a personal battery has enough fuel to burn thru. I think the isolation bags are probably just aluminum(perhaps steel) foil. enough layers to let the infernal thing burn out without catching anything else on fire. You probably still get a lot of nasty smoke.