If Northern Ireland joins the Republic of Ireland to become a United Ireland, will the Common Travel Area be abolished?
CTA, in part, exists because of the fear of a hard border between UK and Ireland. Why do you think CTA will survive if a United Ireland is formed? There would simply be 2 separate countries (well distanced by a water body). No question of a shared border.
On a purely technical note, since the Common Travel Area includes United Kingdom, Ireland, the Isle of Man, and the Channel Islands, a united Ireland leaving it wouldn't automatically cause the area to dissolve.
On a more practical note there would still be significant hurdles to immigration controls between the UK and a united Ireland. The Good Friday agreement allows the people of Northern Ireland to choose their citizenship as British, Irish or both. Forcing people who identified as British to leave would be very unlikely to remain a peaceful solution. Similarly a significant number of migrant workers have travelled in both directions leaving an aging, embedded community.
