Disclaimer: If I owned Harry Potter, it would have a lot more devious plots and hidden stratagems. I think.
Dead or Alive
It was a dark and stormy night, according to the Ceiling of the Great Hall. Hogwarts was feeling anxious, probably. Or maybe just its Headmaster was. Severus Snape stared at the ceiling, studying the swirls of clouds and wondering if the perpetual good weather had been due to the perpetual sugar-high disposition of Dumbledore. He was distinctly happy in all possible ways that man, possibly the one who had coined the new meaning of the word "gay". Ah, well, Lily would appreciate the weather. She liked storms. Not that there was any outside now.
"There are more things between heaven and earth," he heard and his head swirled around to see who dared quote the Muggle author in a Death Eater-ridden school. It was Carrow, who had paused to take a sip of his drink and now continued, "than just flocks of birds and airplanes. We need to keep an eye out for aerial attacks, too, not just land ones."
"They'd never dare show their faces around Hogwarts, not them, these idiots. We've basically won, whatever you might say. Sure, they have their petty resistance, but without the old idiot, they're like headless chickens, we'll catch them one by one."
Snape refrained from telling them not to underestimate the Order of the Phoenix. Let them delude themselves. Let them be weak from carelessness when the time came. He was not proud enough to rub caution into them. Besides, Lily would be annoyed with that and would be very displeased when she saw him. He had every intention to go to her when the entire war was decided, so he couldn't risk her wrath now.
He realized that he desperately needed to get out of the castle and find the dunderheads that were supposed to save the day. Albus had never listened: the children needed training, not cuddling. A good childhood and a quick death were no match for a hard childhood that allowed one to survive. He rose from the table and left. Nobody would question him. They all assumed he had something Headmaster-y to do.
He felt the anti-venom for Nagini in his pocket. It was always good to be prepared. Very prepared. Crazy prepared. Survival was his number one priority. Just as Harry's survival had been Lily's. Not that it had prevented her from being cunning about herself. Spend enough time with a Slytherin and it started to rub off.
He had a small tracking device that allowed him to see where the Dunderheads were at all times. He took the sword of Gryffindor with him, assured that all would be alright. They wouldn't question his lead. They were not as himself, to be paranoid for their own survival. For once, it would be a good thing.
He Apparated to their location in the forest, found a small pond, threw the sword in it and then created a Patronus to lead them. They never questioned him. They never caught the King Arthur reference, either. The doe, that was a symbol of Lily, a lady, a sword, a lake... No? No. Children today don't read.
He sneered to himself, then swirled around on his heels and Apparated again. Lily. He had to keep Lily in mind. She needed provisions where she was, he was certain of that. He'd have to send them. That, and some books. She probably needed a severe update of her own bookshelves. Considering her status, she couldn't very well roam bookshops, could she?
Albus's crazy plan had better work, or the kids would die, they'd lose the war and it would all go down the drain. He hated Albus. Bloody Gryffindor. Had to die stupidly like that. If he had been in his place, he'd have checked the bloody ring, used the goblet to throw the poison out and not forced a friend to murder him. It could all have been avoided. But Albus had always been slightly suicidal - "Death is the step towards a new great adventure". That was his way of saying he wanted to see what was beyond so much that he was willing to commit a complicated sort of assisted suicide.
Severus's motto about death: "Death might be an interesting adventure, but you should really hang on to life and live it first."
He returned to Hogwarts feeling annoyed and tired. It was going to end bad for somebody, he was sure. There would have been so many ways to bring the Dark Lord down through cunning, less risk and without involving adolescents. But all had to be done Albus's way, according to some prophecy, in the best way for helping the kids grow up.
Albus should have grown up. He never had, the old idiot, always playing the sage and having too little common sense. Gryffindors had to get a clue – they generally didn't. Except Lily. Lily got clues. Her husband didn't. Never had. But that was to Severus's advantage, really. He had patience, he had charm, he had elegance, he had everything. James was far, far removed from ever being a rival again. All men were far, far removed from being rivals again.
He smiled to himself.
Severus felt the snake bite him and collapsed. By gods, it hurt, the paralyzing venom running through him. He stung himself with the anti-venom needle, yet still collapsing on the floor. He had to be in charge, he had to take care, to save his own life, to survive, while keeping the pretense up.
The teens came to him, stumbling, afraid, he breathed the select few memories at them.
"Take them," he said, hoarsely, dyingly. They did, then left.
He lifted the wand towards himself, shakily. He could do it. He'd been in worse pain before. If one masters the Cruciatus, all else was nothing. And he'd mastered the Cruciatus long ago, in the same way Potter had mastered Imperius and thrown off the Avada.
He climbed to his hands and feet, then rose himself, transfigured a random piece of paper into the semblance of his own dead self – another strange acquired gift – and Apparated away never to return between the officially living.
He landed in a secluded house somewhere away in Germany, where Lily was watching the proceedings of the battle through a magical mirror that doubled as a window. Nobody noticed the high patch of floating picture, but she skillfully threw her own careful spells around the battle, protecting those she could, but mostly taking care of her own son.
Severus sat down next to her, tired, and took out his wand, doing perhaps much less than her, but having a very valid reason for it. Nearly dying tends to take out your spirits.
They survived, all three of their bloody trio, and that Weasley chit. Mostly due to Potter's guardian angel in the shape of his mother.
When it was all over, he dragged her into his tired embrace.
"How come you always appear with James whenever he ghosts about?" he asked her.
"That isn't me," she explained. "He found somebody else. And I understand that it's easy to take another's shape when you're dead. Forms matter so much less...."
"Who is that, then?"
"Albus's sister. They seem to be having fun."
"Are you going to tell him you're alive now?"
"Harry?... No. I was in a comma when he needed me and not available afterwards. I'd be too... too cheesy. I'd have to explain about you, his father, how it wasn't going as well as could have been supposed, how you nursed me back to life... It's too much, Severus. And we're both supposed to be dead. You're also supposed to be a Death Eater. Let it lie. Perhaps, even later, we'll go out and tell the world – but as for now..."
"You've become Slytherin, my Lily. A Gryffindor would have jumped at the occasion to see her son and friends from the first."
"No..." she answered. "No, they've all felt like dead for me ever since I came back to myself. I... I... Even Lupin, even Harry, all of them."
Severus nodded, his eyes closing. A long day. A long awaited day. And those who were important for her had been saved. He was saved. She was saved. He was a Slytherin, so the rest never mattered.