Robustness against Agent Failure in Hedonic Games

In many real-world scenarios, stability is a key property in coalition formation to cope with uncertainty. In this paper, we propose a novel criterion that reshapes stability from robustness aspect. Specifically, we consider the problem of how stability can be maintained even after a small number of players leave the entire game, in the context of hedonic games. While one cannot guarantee the existence of robust outcomes with respect to most of the stability requirements, we identify several classes of friend-oriented and enemy-oriented games for which one can find a desired outcome efficiently. We also show that a symmetric additively hedonic game always admits an outcome that is individually stable and robust with respect to individual rationality.