Let me get this straight

Mullah Omar died two years ago in a hospital in Pakistan. No one outside of the Taliban knew he died until a few days ago when Pakistani intelligence managed to confirm his death somehow and decided to tell the world. Despite the fact that his death occurred two years ago, the Taliban did not figure out his successor until this week.

Apparently, the group really fine with being leaderless, even as they are prosecuting a war with Afghan government forces, right up until the news of Omar's death broke the other day. It is only then that they suddenly (and quickly) designated a successor.