I think it could safely be argued, that by the start of this mod all the things that lead to the GHA had already happened. Though we don't know the details, we know that Danish vikings had raided France and Britain for decades at this point. Maybe you could make it depend on crown laws in Denmark, so that given certain factors, which should be very likely to be fulfilled, an event chain leading to increased Viking raids on France and Britain will start. The raiders would settle for cash, possibly at an ever increasing price, but maybe if they take enough land they will want to settle and gain claims. Would that work?