The members schedules, addresses, and even levels of commitment to Christ will also change as time passes. This will inevitably lead to people leaving the fellowship. A group should miss, and be saddened by the loss of members. However, it is a normal part of the dynamics of a group and does not mean it is a failure. Inviting others in is of course very important.
New people bring new ideas and new opportunities for growth.
The members of a group need to focus on friendliness when someone new attends. It will take a special effort to do this, but it usually comes naturally. A healthy fellowship will want to be successful and growing. While it is important to have opportunities for new people to join, there are times when the intimacy of established relationships is needed. When this occurs it is all right to close the group for a time.