I would disagree. Heaven is described as being a wonderful place, and the Earth is merely a regular one. There can be a heaven without hell, so long as it's better than the Earth. Satan doesn't fight for God. Satan was cast out of heaven because he actually rebelled against God. If the bible is all true (Which I doubt) then that would mean Satan is actually a deceiver, and one that is meant to pull people away from God's teachings. I lack any way of seeing how pulling people from the path of God helps God. Quite frankly, it seems that would do just the opposite. Now, I ask you to find a way to make Satan's active rebellion against God into something that is actually helping God. As for the "No heaven without hell" statement, that isn't true. In catholic religion, 3 afterlife locations are described. Heaven, eternal bliss, Limbo, eternal nothingness, and Hell, eternal punishment. Without hell, there is still Limbo. Even without Hell or Limbo, an all powerful deity like God could definitely force you into non-existence or even just not let you into Heaven.
Nasty people don't go anywhere in a hell-less existence. If heaven isn't real, then they stop existing. If it is real, the they would just go to either limbo or they wouldn't be let into heaven. You still have not shown examples to support that Satan fights for God, you've just restated that he does. Also, I agree. The bible is largely wrong as it's written, and you neither have to believe in God or the bible.