Lewis the Pius will be known as charlemagne's only legitimate surviving son when he takes over. He'll have to deal with a bunch of male relatives most importantly his sons who do not like his plan for the inheritance. The Viking problem was at the nuisance level of trouble and had there been a continuation of you know by 814 you've had almost a century of really powerful Frankish leadership had that continued I don't think you would have had the Viking age in this time period. Lewis the Pius has a very different job than his predecessors who had to conquer a place he has to rule it.