The battle has already ended.. God exists outside of time though by some mystery the demons are allowed to participate in time where we are. Don't try to comprehend it.. we can't. What is written is being lived by us now. But as for why they don't give up on knowing their defeat.. you have to consider and realize they are pure pride and pure everything that is evil.. they have no reason outside of their resolve which has been decided on.. they will never change once they decide to attack something of God.. it is only God that holds them back from overturning the world. So even though they know their eternal punishment can in a sense increase due to their added 'evil acts'.. they will never trade a 'less intense hell' for not doing the act of evil. Their pride consumes them more than the fire they are in for eternity.