Basically, the last people that speak Continental Celtic are in East Africa. By East Africa I mean Eritrea and Nubia.Let's say it is around the time of the reconquista . A kingdom lies on the edge of the Muslim Empire. That kingdom's language is the only remaining descendant of Continental Celtic languages at the time of Rome.
This is where I leave this part open to the community. Make sure to share your ideas and speculate about this ATL. What would the culture, genealogy, religion, and livestyle of these people be ?