This is hard for some in the church to accept. I often hear pastor search committees tell me that their numbers are down, but they feel certain than when the get a new pastor that some of the people who have left will return. These folks often are disappointed when I tell them that the ones who have left probably won't return, and they might not even want them to. You can't build a church on disgruntled people who are going to leave when they don't get their way.
It is possible that some might return when they hear that the church has new life and some exciting ministries happening. These are often people a church wants to return because of the passion and gifts they bring. From my experience these folks are few and far between.
If someone on a pastor search committee mentions that a number of people have left the church in recent years due to various issues I would recommend the prospective pastor ask if the church has the expectation that he or she spend time trying to get these people to return. There is a very good chance that will be the expectation. If I was interviewing with such a church I would make clear that such work would not be a good use of my time. The people who left have turned their backs on people they probably have known for a long time. Why would they come back because a pastor they don't know asks them to? If they left because they were dissatisfied with things in the church what makes current members think they won't leave again the next time they don't get their way? You can almost count on it that they will. If the committee or church insisted that their new pastor needed to make it a priority to try to get these people to return I would take that as a sign that this is not the church for me. I believe it was Rick Warren who wrote that we are called to be fishers of men, not corrallers of old goats.
There is much a new pastor needs to do that will produce much better long term results for a church than trying to appease a bunch of disgruntled church members who have left the church. The new pastor needs to learn as much as possible about the people who are there, the community in which the church is located, and begin to discern where God is leading this congregation. These are the kinds of activities in which the pastor needs to invest his or her time.