People from the Eastern continent fleeing in terror from his initial attack would easily spread the word to all three other continents very quickly. So it's very possibly that virtually everyone knows, unless their kingdom is 'undesirable' for refugees to want to settle in, but even then it would only be a matter of time. So anyone can just assume that their characters and current hometowns are very well aware of what is going on, though perhaps not aware that the first attack against Rumple has failed. Also it won't be readily evident where he has his sights set next, so that will add some ambiguity to it and give everyone a reason to want to unite and create a small army of mages as a power base to defend against him rather than remaining spread out and vulnerable on their own.