Irene Adler in Sherlock Holmes:A Game of Shadows

Mother Firefly in The Devil's Rejects

Vanessa Kensington (Elizabeth Hurley) in Austin Powers 2. Though technically she was (according to the movie) a fembot. Except the character had a mother in the first film. And frankly that "revelation" set up the soulless nature of the AP sequels.

Although the character didn't die, it's a surprise in Superman II, that



...considering the character's prominence in the first movie and the way the sequel's story was progressing.

Crossbones in Captain America: Civil War.

I heard Ned Beatty hated that role and that's why his character was cut during the sequel.

And in Superman III, Lois is quickly written out.

IMO, the disposing of Han Solo in TFA was "unceremonious."