So...Billy still dies, but...what if the Russians take him. Billy becomes 'Project Lazarus'. So, he is brought back from the dead...and he has powers now. Like Eleven. For the first few months, he doesn't speak, doesn't remember anything. But when his memories do start to come back, the Russians work on...trying to keep them from coming back.
So he starts to fake it. Pretends he doesn't recognize the girl in the photo when they show him a pic of Max. Pretends he doesn't recognize the name Steve Harrington (because they actually did their research)
And they only call him Lazarus and demand he do things. Like turning the lights on and off. Or crushing a coke can. Mostly, he fucks with them and spends hours when they aren't testing him thinking about home until he is strong enough to escape.