Akatsuki just had to save his sorry butt from the 5 hokages cause he was weak and used the advanced justu Susano without knowing the consequences. HOW STUPID CAN YOU GET EMO KID! He ran out chakra, if he wasn't so important to their plan, i would just say let sasuke die and get what he finally had coming to him! Another reason unfortuantely if he did I fear the seris would end alot sooner.