Like many terms in the bible there is room for multiple meanings of church. Body of believers. Gathering of Christians and non-Christians that either aren't evident or who are openly inquiring into the gospel. Many are called but not chosen. Called out = ekklesia. It might even be possible to escape the pollution of the world by knowing Jesus then get entangled again (wiser souls than I can debate whether that's an 'ypothetical).
Yes, Jesus speaks of that somewhere, sweeping out the house of demons, then they come back and are worse than before.