In zero gravity, BJJ would look very different. Mostly because there'd be no advantage to being 'on top', as you wouldn't have gravity on your side to increase your pressure. BJJ would become much more about submitting positions wherein you don't rely on top pressure or the ability to move on the mat (e.g. hip out), things like the back, leg attacks, and front headlocks.
Fighting in space is actually kind of a fascinating thought experiment because so much of what we rely on in fighting is gravity and, when you're talking striking, friction with the canvas neither of which you had in space. What would striking look like when you couldn't push off the floor for weight transfer or rotation, and when you hit someone you couldn't brace against the counterforce from the blow? I tend to think it would be almost useless other than dirty boxing style strikes where you have a grip and use that to pull him into the strike.
And yes, I do drugs.