It'll be pretty ironic if he dies offscreen considering we're getting two new villains. But likely he'll go down with his ship or something not too graphic. I know he has many fans online, but in the context of the film I don't think he was important enough that they're going to spent too much time on it. His role is on pair with the old guy in New Hope and he'll likely get a similar death to him.
Re: General Hux's eventual death