This article from Thom Rainer is a sobering read. Although written from a US perspective, I think it is likely to be very true of the UK situation too. Certainly, there are things I recognise as I read the article.
I want to add a qualification and then consider how we respond. The qualification is this. If Thom Rainer reckons that about 20% of congregations will not return after the Pandemic, then don’t assume that this will translate to 20% of your church. Some churches will return out of lockdown in a much worse state than that whilst others will be healthier having retained more of their members. Indeed some churches may even have grown.
Now how do we respond to the situation. Well, very simply, my advice would be not to change anything. I don’t mean that you should not assess, review, reflect and prayerfully respond to issues in the life of your church. We will want to ask questions about whether some people left because they were unhappy highlights real problems rather than simply accusing them of beinfg discontent. We may want to ask questions about why some people were on the fringe, never really connected and maybe never converted. How were we actually doing in terms of discipleship before lockdown?
I don’t mean that we shouldn’t be proactive in reaching out to people. These figures should spur us on to make disciples, to follow up on the wandering sheep, seeking out the prodigals. I suggest that we all get our copies of Richard Baxter’s The Reformed Pastor down from our shelves and dust them off. Lockdown has also meant new opportunities to reach people with the Gospel and tell them about Jesus. Those are often people who would not have come into our buildings in the past. We need to seize the opportunities that God is giving us. That also means that we need to be doing some careful sifting too. It is no good patting ourselves on the back because we are getting lots of online visitors if those people are Christians from other churches. Even if it leads to them joining us at the end of COVID, it will not be the kingdom growth we are looking for. Indeed, I suspect that of people do join us as we return to our buildings from other churches then they will have moved on again in another two years.
What I mean is this. COVID-19 may have sped up the decision making process for some to leave and it may have compressed a lot of departures into one period of time. This does mean there will be a bit of a nasty shock for churches and we need to prepare for the emotional bump and indeed the practical bump as we experience a loss of people to help in particular ministries and a loss of finances as people giving move on. However, as Rainer makes clear in his article, these were people that were going to leave. The underlying issues that led to their departure were always there and would have come to light soon enough. So, all the things that I mention above should be things we are doing anyway.
Of course if we haven’t been doing those things then this might be the wake up call we need to start!
 And even if we see new people come in, they won’t just slot into serving and giving in the same way.