Sasuke dies at the age of twenty-two, in the place where everything began. After years of planning and gathering a lost generation of shinobi as cannon-fodder, he marches into the Valley of the End, prepared to destroy what he once called home. When he reaches the great statues, he sees only one person waiting to meet him.
Tsunade stands tall and proud, the very picture of an avenging kunoichi. "Come, Sasuke," she taunts. "You're not afraid to fight an old woman, are you?"
Sasuke motions his army back and draws his blade. Tsunade looks intently at him while she draws chakra into her clenched fist and says, "You should never have come back."
Sasuke snickers at her, confident that he could never be killed by an old woman. An ugly grin stretches across his face while he replies, "Why not? It's not like I'll be deterred by a single kunoichi well past her prime!"
Tsunade crosses the space between them in a flash, plunging her hand into his chest and pulling out his still beating heart. She slits his throat for insurance, and lets his limp body fall into the still water. She throws his heart in after him, musing with a sad smile, "So he did have a heart."
The funeral is the next day. Sasuke is buried without ceremony in an unmarked grave on the outskirts of Konoha's cemetery. He died as he lived- a traitor. Only two people attend the funeral- Tsunade and Kakashi. Naruto lay paralyzed and comatose in Konoha Hospital, the side effect of one too many rasengan shurikens. Sakura died a hero in the killing fields of Otogakure. She sacrificed herself killing Kabuto in defense of her genin team. Tsunade and Kakashi are only there because they always finish what they started.
Walking back to his cold, empty apartment Kakashi ruminates on Sasuke. It's taken him a long time to assuage the guilt he held for what he saw as his part in Sasuke's ultimate betrayal. And it's taken an even longer time for him to see what Naruto and Sakura never could: Sasuke never wanted to be saved. He carved his path in stone long before Team 7 even existed.
Sasuke, Kakashi mused, was just another fanatic willing to destroy anyone and anything that stood in the way of his goals, even his own soul. At the heart of hearts, he was just your common, everyday, garden variety monster.
Kakashi trudged up the stairs to his apartment, expecting to find it dark and cold. A light was on and the subtle sound of tuneless humming drifted into his ears. He drew a kunai from his belt and slammed open the door.
"Oh there you are Kakashi!" Gai exclaimed. "I was just making miso with eggplant- your favorite," he continued in a much milder tone.
Kakashi sniffed the air experimentally and sure enough, the apartment was filled with the tantalizing aromas of miso soup and eggplant. He stepped up next to Gai and wrapped an arm around his waist. He leaned in for a quick kiss with a smile. Welcome home, he thought to himself.