My theory

8 needs to drop the meat wall to allow everyone to get into Hawkins lab to save Holly and the other kids, this will set the stage for 11 to fight Henry as Vecna in the Hawkins hospital in the upside down and kill him where the portal opened that sent him into dimension x to become Vecna and this would erase everything because it's stuck on the same date when it happened. Meaning that eleven would have never met the boys and will wouldn't have been taken.