Complex sentence: However, though the Pictish language did not disappear suddenly, a process of Gaelicisation (which may have begun generations earlier) was clearly underway during the reigns of Caustantín and his successors.
Split into simpler sentences: However, though the Pictish language did not disappear suddenly, one could imagine a steady progression of Gaelicisation (which may have begun generations earlier). It was clearly underway during the reigns of Caustantín and his successors.