There's got to be a multi-pronged approach don't you think well the Byzantines will do a lot of the same things that they do in the west. Byzantine diplomacy is famous they'll have these people fighting and dying for their empire before this whole thing is over with. If Vikings keep raiding your coast you're gonna start trying to figure out how you can counter punch or at least defend yourself. The early nights in the middle ages and feudalism and castles was a direct outgrowth of these Viking attacks.