I would terminate one of our people if they acted (or did not act) for the reasons OP states. A coworker is a coworker until he is not. Either the coworkers or OP need to leave if it is as bad as he says.

But, marooning colleagues is contrary to the business interests of the employer. Saying that it is not OP's job to warn the colleagues is as infuriating to a senior executive as having wait staff at a restaurant say, "it's not my station" or customer-facing employees who refer to their employer as "they" when discussing a customer issue.