Well, tbh my 18 month old doesn't like bed either. We have had to remove the door handle from the inside his bedroom because he opens it and runs out laughing

His new trick is to bang his head on the floor...all for attention! Me being me, I'm terrified that he will do some serious damage to himself and go up and move him back into bed. I've stopped talking to him now when I go put him back into bed. I don't say night night or tell him off, just pick him up and put him in bed and shut the door, it helps a little, as in he only tries it a couple of times again before deciding I'm not going to give in and take him back downstairs or in our bed. Sometimes he is in a mood to get what he wants but we try to stick to just putting him back into to bed. Its not too bad for me as George can't talk yet, but I could imagine an 8yr old being able to give a bit of verbal and be a lot harder to put back into to bed
Good luck, I know it wasn't exactly fantastic advice, sorry