The losses pile up before Sam ever gets to the end of New Mutants.

The losses pile up before Sam ever gets to the end of New Mutants. Doug dies during the Ani-Mator story. Later, the Genosha crossover kills Warlock. Illyana is no longer with them as the teenage teammate they've known, Dani stays in Asgard, and other members leave or become separated from the group. Sam isn't leading the same set of kids who arrived at the school together. He keeps having to adjust to people being gone, including people who aren't coming back at the end of the next fight. Bobby is especially important to him. They come from completely different backgrounds, but they've become close friends. That makes Bobby's decision to leave in #99 more than another change to the cast list. By then Sam has already watched the team lose its original school arrangement, its teachers, and several of its closest relationships. Staying with it means choosing to keep going with what's left, not pretending everything is still the way Xavier set it up.