God 1 - Devil 0

There are some times in life when I actually start thinking about who God is, what is actually happening, and how that effects us.
This means I start asking questions.
Here is one.
I know that on the cross Jesus said "It is finished!" and I hold on to that truth. It is finished, he has done it, death is beaten. We no longer are condemned by the law, we are no longer slaves to sin, we are free, we are alive in Christ, we are living life in all its fullness and will be made perfect in his glory at the end.
But what happens to those who are not saved? We know that Jesus fought the Devil and won. When someone is not saved what is happening in them going to hell? (Do they go to hell?)
My logic (which is often dodgy) tells me that if the devil has been beaten, he has been beaten, Jesus did it, GAME OVER. But we also know that we need to be prepared for battle (armour of God), does this mean there is potential to lose?
God and the devil are not even in the same league, they are not competing, never were competing, never will be. But if someone goes to hell is God's will fulfilled? Does he not wish Salvation on all men? Is hell a time when God loses? And if people do end up in hell is that the devil becomming victorious in that individual battle?
So my question is this ... Is hell, as a necessity* (rather than a punishment), a part of the war (against the devil, against evil, against death) that the cross can never win?
I want to say no. The cross is enough. God's grace is enough, but in saying no does that mean all are saved? Please give me a kick if I am being foolishly stupid or blind. Or if I am being just foolish. Or if I am barking up the wrong tree.
*I use the word necessity as I realise that God cannot be near to sin, and my theology would say that only Jesus can wash us of sin, so hell is a necessary outlet.