Jessica should have never been killed.
She was the hero's love interest, essential part of the show. The captain's daughter.
Killing her off was just lazy writing, she could have been kidnapped numerious times playing up the movie cliche on how the hero has to save his girlfriend from the badguys. Would have loved to see a Die Hard moment where McClaine shot Hans Gruber off the roof to save his wife. Ryan and Jessica had a very interesting relationship and would have loved to see if jess could have put past him as the mole cause she has real feelings for him.