I also liked that moment in the DotF script, but it would be hard to set up Hux even having a lightsaber, as well as filming a brand new scene with him using it. That’s why I think it would be easier to replace a few shots and see him engulfed by the explosion. Since Hux is responsible for the stormtrooper program, it would be really fitting for two ex-stormtroopers be the ones that get to kill him off. There’s also an extra bit of irony in the fact that Hux was aiding the Resistance in order to undermine Kylo Ren and eventually replace him, because by helping Finn escape earlier in the film to screw over Kylo, it allowed Finn to return and kill him. I just like the idea of Hux’s spite for Kylo Ren and his own creation (the stormtroopers) being his downfall.