IIRC she said she wanted to be the mo-cap character? I remember her giving an interview before the movie came out where someone basically said the same thing to her and she was like “I wanted to try this type of acting, because it seemed like a rare opportunity, especially for something like Star Wars.” I might be misremembering that, but I do remember thinking something similar before I was told she really wanted to do it, and was surprised.
I guess the current rumors are that Maz helps in the big battle against the Emperor in the third act, shows up to help with a squad of pirate warships or something like that. I don’t know if that would really cheapen anything. Seems like a decent payoff to the First Order wrecking her castle.