Sometime in the future...
Sam and Dean were well into their sixties, sitting upon a porch out in Colorado. They had bought the ranch-style house with money from Dean's life insurance policy when he had died for the dozenth time. Dean brought a bottle of beer up to his lips and drank. Azazel was curled up in his lap, snoozing.
"When do you think that cat's gonna die?" Sam asked, scratching his balding head.
Dean set his beer on the table in between them. "Soon, I reckon."
There was a rustle in the bushes. Sam took up a shotgun and fired into it. A strange body fell out of it and the Winchesters resumed their conversation.
"Do you suppose that Cas did something to make him live longer?" Sam questioned.
"I reckon," Dean replied.
Sam furrowed his gray eyebrows. "Perhaps that demon is still in there."
"Don't be so paranoid!" Dean pat Azazel's head, waking him up. The cat began kneading Dean's jeans. "Ouch."
"Well, I just don't want to be on my deathbed when that cat gets up on me and says, 'I'm still here, boy,' and then I die without being able to tell you."
"You're such a drama queen," Dean slowly shook his head and stroked the cat, who was chuckling on the inside. "Besides, I reckon I'll die before you, little brother."
"Don't say that."
"I reckon we should die at the same time."
"Agreed." Sam laid the shotgun back down, took up his own bottle, and drank. "And stop reckoning."
"Get rekt."
A breeze blew, disturbing a wind chime that played a nice melody. Azazel jumped from Dean's lap and stretched, tail raised high in the air. Although he had outlived all other cats, he still felt the effects of aging. His chin and underbelly were white and he could no longer hunt animals and leave their remains around the property. He thought that Sam had suggested a last good joke to play on the human, but Azazel was unable to communicate verbally anymore as he got older. He went out for his nightly walk in the woods as the sun set.
Meanwhile, the Winchesters went inside their well-earned home that was also well-warded. Castiel, still youthful, poked at the flames in the fireplace.
"When did you get here?" Dean asked.
"A while ago," Cas responded vaguely.
"Is there trouble?"
"No."
"Good!" Dean sat in his armchair in front of the fireplace. "There ain't been no trouble for...five years, I reckon."
Sam rolled his eyes. Ever since they moved out here, his brother had taken on some kind of country-westerner persona. "We were talking about when Mittens is going to die."
Cas' brows raised, but the brothers couldn't see because he was still poking at the fire. "Well, I have no knowledge of that."
"Sammy's a paranoid drama queen," Dean said. "I think he's getting dementia. Time to send him to the nursing home."
Sam grabbed a throw pillow from the couch and chucked it at him.
Azazel returned through the cat door with a dead bird in his mouth. He hadn't caught it himself; he found it already dead in the woods.
"Good boy," Dean stated as Mittens laid it at his feet. "Y'know, I reckon I wouldn't actually care if that cat was really the Yellow-Eyed Demon, who eventually became good."
"I'll send you to the Home," Sam teased.
Cas shifted uncomfortably, as this topic hadn't come up in about thirty years. He turned around. "Stranger things have happened."
They all nodded solemnly, even the cat, who had been a source of comfort over the many trials of the Winchesters. Everything seemed to start with him, and it would end that way, too, as he was there for them as they calmly passed away in the hospital several years later. Then Castiel carried him up to heaven, where they remained together as a confusing family. Sam and Dean didn't know anything for about two hundred years. Then Cas spilt the beans. He had literally spilt some beans when they were playing bingo, beans going everywhere, when Azazel suddenly meowed, "Jet fuel can't melt steel beans."
The End