Empire was dark enough as it was; doing that would have lost a large chunk of the audience (me included). Nothing to do with Leia being a woman; you simply don't make a hero who's the clear focal point of a series, and then kill him OR her in the middle of their journey once you've gotten past a certain point. Kill off Luke in Star Wars, okay, you could probably do that, but you really should do it at most maybe 3/4 of the way through so that we can re-focus and find the REAL hero of the plot, but not after you've finished the first movie, and then gone through 95% of the second.