It is important, in situations where teams of agents can commito joint, long-term objectives, that the agents be able to identify when the team objective is no longer important, or is futile. Prior work has typically assumed that agents should believe that joint commitments hold unless explicitly told otherwise by other agents. In this paper, we argue that this assumption expects too much from the communication channels and from agents that initiate the abandonment of the commitment. A more general, robust method for monitoring a joint commitment is to make each agent responsible for acquiring evidence that supports or refutes the contention of the sustained commitment. While this evidence can include explicit messages from others, it also can include observations made by the agent and interpretations of those observations. We thus build from formal notions of commitment to collective goals, and conventions for explicit maintenance of beliefs about commitments, and extend this work to allow observations and the consideration of imperfect communication channels. Our approach has been implemented and tested in the application domain of cooperative robotic reconnaissance in a sometimes hostile environment.