Communication is the most important part of working in a team. Everyone has their own life and own responsibilities but they must also understand that their team needs their commitment as well. When one of your team members is having trouble communicating, the first thing you must do is reach out separately to find out what is going on and how to resolve it. If the issue does not resolve itself and milestones are being missed, the next step is to inform the PM of the problem. Once that is done, the rest of the team members should continue to work with diligence and relieve the distant team member from their responsibilities and replace them.