It's not that Lydia is bad. The Walking Dead comics present her with various challenges and choices that make her character more layered and not easily defined as purely bad.
In the comic, Lydia's staying after Pikes was a result of multiple factors. It involved her changing relationships with key characters and the evolving dynamics of the group's survival.
Michonne does die in the comics. The circumstances surrounding her death were quite dramatic and had a significant impact on the story's progression. It happened during a major conflict with other characters.