You don't have to wait till Friday for strike. You can do all the Eris quests aside from the Xur one and still get the quest in which Eris tells you to kill omnigul. A level 26 strike will unlock on earth. You can do the nightfall/weekly and still complete the quest. P.s. The nightfall version is really REALLY brutal. Who thought it was a good idea to make it arc burn and make a wizard the final boss?