"We did it, we bashed them, wee Potter's the one!
Now Voldy's gone mouldy, let's have some fun!"
JK Rowling, Harry Potter and the Deathly Hallows
Peeves had been hiding during the battle. He did not want to get involved in the battles of the wizards. But he had been quite concerned about it. He was only a mischievous poltergeist, but he did not want the castle destroyed. It was his home after all.
The moment he had seen Lord Voldemort, he had zoomed away to safer hiding place. He was a poltergeist, but he was not at all evil. All he did was a little swearing. A few jammed up doors, here and there. Dropping water bombs. And once, assisted by Professor McGonagall no less, he had sent a large chandelier smashing to the floor. Good times.
But now Voldemort was dead, and the battle was over. Voldemort was not the only one dead though, students, teachers and members of the Order of the Phoenix alike had all succumbed to the Death Eaters that were attacking the school. Peeves emerged from the hiding place he had chosen, and saw in one moment the chaos and devastation that the castle was in. But Peeves did not really have complex feelings, and so all he really felt was a bubbly euphoria that he who must not be named was now gone. He knew though, that he would probably not be welcome amongst the grieving, the injured and the dead.
He floated away, cackling loudly, a smile on his lips, and singing the words: "We did it, we bashed them, wee Potter's the one! Now Voldy's gone mouldy, let's have some fun!" He was only seen by Harry Potter, the true hero of the battle, who, in spite of it all, grinned as Peeves bounced by.
Peeves dashed out of a broken window, smiling with delight. In all his time wreaking havoc at Hogwarts, he realised that he never had actually once been out into the grounds. Think of the fun he could have!
In the castle, tears and blood were still flowing. But as the night gave way to a pale, watery morning, the brave wizards and witches who had fought gave a mile of relief. There may be testing times ahead, but who cared about them? Only one thing mattered now, and the thought of it filled everyone's hearts with gladness.
They were free.