Just to clarify, the seven churches of Asia aren't the first churches described in the Bible. That was the church in Jerusalem, as you can read in the Book of Acts.

But regarding the seven churches of Asia, Christianity - and most of those churches - remained strong through the Byzantine Empire. After the conquest by the Muslim Turks, it started gradually declining (to summarize many centuries in a few words), but remained a live presence until the Greek-Turkish War in 1920. The war ended with a population exchange, which caused many of the churches to vanish and others to decline as the Christian Greek population moved en masse to Greece.

If you're interested in the history of the specific churches, Wikipedia has links to decent overviews.