Sales of The New Mutants had slumped for several years in the late 80’s, but took a sharp upturn after Rob Liefeld took over the penciling and co-plotting chores at the end of 1989. A new mentor for the group, the mysterious mercenary Cable, was introduced, further helping sales. Over the next year, several longtime team members were written out or killed off. However, the relationship between Liefeld and Simonson was fraught with tension, and Simonson claims that Harras dealt with the situation by rewriting her plots and dialogue so that the characterizations did not make sense: “Although I wasn’t being fired, I think I was being shoved out the door with both hands by Bob Harras. Bob was only doing what he had to do, I expect, which was make Rob Liefeld happy.” Simonson eventually gave in, leaving after issue #97. When Liefeld and Fabian Nicieza, who wrote dialogue based on Liefeld’s plots, took over as writers of the final three issues of the series, they included several harder-edged characters.
The New Mutants was cancelled in 1991 with issue #100, but the new platoon-like team formed by Cable continued in X-Force, a successful series (whose first issue sold approximately one million copies) that would continue until 2002, and feature a variety of the former New Mutants cast.