LARAMIE, Wyo. — Lee Child had two ideas for how Jack Reacher, the toweringly popular hero of his long-running series of thrillers, might die. First he thought Reacher would get into one last fight and bleed out on the bathroom floor of a filthy motel. But when he said so at book events, fans seemed viscerally disturbed by the idea, truly distressed, in a way that made him think that to follow through on it would be “gratuitously nasty.”