This is largely based on my experience with Rev. Laura Lin's (whose chief problem is idolizing gifts/talents) church but not limited to hers only in my experience. I have already criticized Lin, so there's no need to do any stomping anymore. There there is judgment, there must be room for calmness.
When people say they are leaving a church that they've been around for a while, then we can consider the following:
These are folks who have been around the churches for a while. And they have especially voiced such concern or "ultimatum" to the church leaders/pastor. Therefore, I am not referring to those who have suddenly gone silent for no reason, which they truly meant: We will come when we come. Perhaps they found a better church but wish to maintain some sort of life line connection to their previous churches, hence the silence. Whatever reasons they maybe, these people do not wish to make clear whether they will be coming or not.
No I am not talking about them. I'm talking about those who specifically mentioned to pastor and leaders (and basically anyone), indicating that they have no desire to return. Now let's eliminate one category of these as irrelevant to this topic: Those who have moved away, or for whatsoever reason it is, causes them to not able to attend anymore EVEN IF THEY WANT TO. I'm also not referring to pastors or preachers. These do not get to choose to leave in ordinary circumstances because they are like parents to a family. I do not believe that there is such calling of God that would call a pastor to leave the church for another like a father leaving a family for another.
Alright, now we've filtered out the unnecessary categories, let's get down to brass tacks.
Those who specifically clarified that they won't be returning to the said churches that they have been attending for a while, as if they were already members, are those who obviously meant that there is something wrong going on. And it is the church's responsibility to seek this out. What is the reason for declaration? For who else should care about this? Certainly not the one who already said they are leaving. God? (No wonder churches in the West sank into individualism - and it's a shame for Chinese churches to follow suit, because this is the one thing Chinese church and culture has triumph over Western churches - family-like caring).
Now, to be fair, it's not necessarily that it is the church's fault when some long term members say they are leaving. It could be the fault of the ones leaving. For example: Music isn't modern enough, did not feel welcome, talking about Bible too much, age group differences, cultural differences, etc. These problems I attribute not to the church in general. Nonetheless, the church should still try to communicate with such goats, just so in case that they may actually turn out to be sheep. Confused sheep.
That leaves the part where it is the church's own fault, when someone say they are leaving. Therefore, it is the church's task to find out why, as always whenever a member leaves. It is not necessary the burden of the one leaving to make his reasons clear, especially when he believes that it is pointless or when there is no fellowship. A church however, cannot function like such individual, believing it to be pointless to seek out why someone leaves, for the church has chiefly, a Gospel responsibility. Believer or not, the church should seek that person out to confirm that his departure is solely his own fault, that all attempt to reconcile has failed. The worst thing the church can do, is to make false assumption of why a person is leaving and leave it as that without any communion. First, this shows if the church ever cares at all if anyone stays or leaves, truly care and not just hoping for numbers, second, this also shows if the church ever concerns her own shortcomings.
We have touched on the church's role in this. Now what about the one leaving? What reason should justify one leaving? Obviously in this case, is because that there's some short comings in the church. Lack of caring, age/culture group differences are top on the list, but insignificant, I believe. They are popular but not good reasons enough to leave a church. For the church is a fellowship of saints, not a Caesar's Hotel. The other side of extreme reason possible is that the church has become a cult. Practicing heretical views. This is rare but will validate people leaving so much that those who stayed should really be viewed questionable.
So what else could be a good reason to leave a church? I have no set principle for this. But in general, I would say that when a church is dying and nobody cares. How can a church be dying? When she is no longer Gospel-Centered. Everything we do in the church, is the fellowship resulting from the Gospel, that is the beating heart of all. Without which, the church cannot seriously be talking about evangelism but mere recruitments, marketing strategies, tribalism. Many churches would be fooled into thinking that they are Gospel-centered, but they are actually just Gospel-supporting, because when looked upon closer, that which should be seen in Gospel-Centeredness does not match up with a Gospel-Supporting-only church. Members of a Gospel-Supporting church do not usually know their basic Bible knowledge as they should: ie. who is Moses? Especially after being member of that church for well over 30 years. And when push comes to shove - those members would insist: All religions are good, which may be a tell-tale sign that the church is heading towards heresy, if not already is in.
Last but not least, when a person leaves a church for this very last reason, he should show some discipline of care for such a church. To pray for the church. To check up on such church here and then. Not hoping her to fail, but hoping that God would strike such a blow in her heart that she repent. The wise smacking love of care.