I always feel a bit sad when this happens. In some ways, it feels like a family member has disowned us. They've decided they don't want to hang out with us any more, they'd rather spend time with a different bunch of people.
I've noticed over the years that there are a couple of ways that people tend to leave when they are moving on to another church. One is the very public dummy spit about what's wrong with the current church. In one case I'm aware of, a guy who was rostered on to pray got up and mid-prayer had a bit of a meltdown about how the church was grieving him and he couldn't stay any longer. Not ideal. A little bit awkward for those of us sitting in the congregation who really had no idea how to react to this. Do you keep your eyes closed or do you open them and look around to see what others are doing?
The other form of departure I've encountered is the quiet disappearance. People just stop coming, you think they must be on holidays or something, and then you realise you haven't seen them around for a long time. Eventually someone makes a comment about them having moved to some other church, or the penny drops in some indirect way. In this particular instance, I saw that their photo wasn't in our new church directory which came out last week. And then I asked a friend of mine about them and discovered she'd sent them an email saying she'd been missing them at church. She'd received the response that they were away at the coast for the weekend. Nothing more than that. We haven't seen them since they disappeared. Well, except on Facebook. More on that later.
I'd like to suggest a better way to leave. Be upfront about it. Not in the public dummy spit kind of way. And not necessarily even with everyone in the church, but I think for those people who've known you for a while it's kind to offer some sort of calm and reasonable explanation. It prevents those confused feelings on the part of those you are leaving behind about why you've gone. The most important person to provide this explanation to is the pastor of your church, and he can decide whether the reasons should be shared about it or not. Even then, I think some kind of brief comment up the front about the people no longer attending can be helpful. It provides closure and removes the uncertainty (and hopefully decreases the gossip) about what's happened.
People change over time. I get that. Sometimes people find their needs may be best met in some other church family or denomination. A new season in their Christian lives and growth may be what's required in some instances. But for those left behind, it can really hurt if no explanation is provided about what's happened. In one case, a family left our church and their kids were quite good friends with our boys. Luckily our guys don't tend to ask too many questions, but if they did ask where they'd gone, I wouldn't be sure what to answer.
Just one thing that you probably shouldn't do if you are the person leaving and moving on to another church. Avoid taking to social media (Facebook, twitter, blogs or anywhere else) to say how fantastic your new church is and that the people, the message, the singing or whatever are absolutely wonderful compared with those "other Christians" who do things differently. It's all too painfully obvious who you are talking about.*
*and yes, I do realise that this could be a case of the pot calling the kettle black here. I'm trying to work out whether to say something and if yes, then how or what. Happy to take suggestions....