Well, if the Scots had never invaded Pictland, and settled in Dal Riata, they would not have had the opportunity to take over when the Picts were knocked back on their heels by the Viking raids/invasions. Although Kenneth MacAlpin of Dal Riata, who seized control of Pictland at that time, was as much Pictish as Scottish in his ancestry, he (and his successors) chose to emphasize the Scot culture and language over that of the Picts, and as a result the Pictish language simply fell out of use during the following centuries as the ethnic Picts switched to the culturally dominant Scottish language. From what I can tell, the replacement of Pictish culture and language by the Scottish version was an perfect example of historical contingency -- had certain events happened slightly differently, we would still have "Pictland" on all the maps.