Well... It's going to be a surprise, mainly because I don't know whether I'll kill Menmar's Boss Villain... It's something I'm think about yet. I am not a villain-killer per se, but I believe some characters can be redeemed and others cannot, and that's how I approach villains.
When killing is involved, it always takes place in an ironical situation for said villain, in a scenario where they should succeed, but they don't. I like poetic justice, I think most people do.