It's not really a "the lich king is only arthas now". Unless someone else takes Ner'Zhul's place, there is no Lich King. There is no Scourge. Ner'Zhul never made the pact with Kil'jaeden. Unless someone takes his place, Warcraft 2 never happens, much less 3 and any of the stuff afterwards. I doubt they will go very far with the timeline, but if we go to Azeroth-2, Lordaeron isn't the Plaguelands, Dalaran is still on the ground, and if you're a Tauren, you probably need to declare "I come in peace" unless you want to be eaten.