This is not a complete answer but it's been 7 hours and nobody has answered at all, so I will throw in what I know. There were certainly wars between Northumbria and Pictland and between Dal Riata and Pictland, and in the 12th century Henry of Huntingdon wrote; "but we see that the Picts have now been wiped out and their language is totally destroyed so that they seem to be a fable we find mentioned only in writings." However, the Pictish people weren't actually destroyed. Their process of 'nonemesis,' losing their identity and becoming part of the larger kingdom of Alba, is complicated and difficult to study due to the dearth of evidence from Northern Britain in the time period during which they disappeared, the Viking Age. For a complete answer to the question, I'd recommend reading Alex Woolf's book, From Pictland to Alba, 789-1070.