Thy Will Be Done
In the end, the change is a tiny one. It takes no more than a simple nudge, just the barest suggestion at the right moment, to ensure that Dean distracts Mary before she can change the batteries of the baby-monitor. She forgets until John has to wake her in the middle of the night because she didn't hear Sammy screaming.
On April 27, 2007 Sam Winchester goes missing after a friend's birthday party. It's not noticed right away because the party's on Friday, and his friends assume that he decided to stay home with his fiancée when he doesn't show for classes on Monday.
On May 2, 2007 Jessica Moore is found murdered in the apartment she shares with her fiancé. It's clear that she's been dead for several days.
The police suspect her fiancé, but there's no concrete evidence and the young man in question is missing. Eventually, both are added to the growing number of cold cases.
On May 2, 2008 Dean Winchester asks Carmen Porter to marry him.
They've been living together for three years, Dean hasn't touched alcohol or gambled since his brother disappeared, and she loves him as much as he loves her. She says yes immediately.
Also, she thinks she might be pregnant but she hasn't gotten around to checking yet.
On September 18, 2008 Dean Winchester and Carmen Porter get married in a civil ceremony. They invite only their closest family and friends, so it's a very small wedding.
Carmen isn't pregnant, but she's decided she'll bring up the subject soon.
It's a great surprise to everyone when Carmen gives birth to twins, triplets and twins, because that kind of thing usually runs in families, and it's never run in either of theirs.
The two eldest, Micah and Lucas, are identical physically and polar opposites in every other way. One of the few things they share is their love for soccer.
The triplets, two girls and a boy, are Susan, Deanna and Jonathan, and they often act like three independent limbs of a single organism. They are also the sneakiest pranksters who ever lived.
The two babies, Jessica and Samuel, go on a road trip to New York the summer they turn eighteen, and horrify their parents by never quite stopping instead of going to college. They rarely tell their family where they go and never what they do, but when they come home for Christmas the first year, Mary takes them aside and gives them a pair of necklaces and two thick leather-bound books. One is filled with cramped handwriting and sketches and newspaper clippings. The other has only a short note written on the first page, in Mary's handwriting: Watch out for each other. Trust no one else. Double-check everything. I love you. Grandma
She doesn't say a word, just goes back into the kitchen to keep Dean and his first granddaughter from eating all the cookie dough. She cuts them off whenever they ask questions about things that live in the dark.
Dean dies in his early sixties, of a heart-attack. The doctors say it was a flaw in heart that he was born with, and he's lucky it hasn't made itself known before.
Mary dies less than a year later, and though the official cause of death is old age, her family agree that she just didn't want to live anymore after her husband and both her children were gone.
Carmen lives another ten years before she, too, dies. There's some speculation of foul play, but in the end her death is pronounced accidental, if tragic. No one could have predicted that she'd fall asleep in the bathtub and drown on the anniversary of her husband's death.
In 1973 Mary Campbell and her father have no reason at all to go to Liddy Walsh's home.
The day after John Winchester asks his girlfriend to marry him (and she says yes), he gets word that his older sister is dying. The daughter she gave birth to during the night is alright, but the doctor and the midwife are in agreement that John's sister will die before midnight.
When the man with the strange eyes, that are sometimes brown and sometimes yellow, comes to John and offers to save his sister John agrees immediately. He doesn't think about what the man asked for, even when the ten years are up.
In 2007 a girl named Ava Wilson accepts the gun the demon gives her and nods at him. Then she shoots him in the head.
Considering how difficult it was to pinpoint the ideal moment to make the change so that the rest might fall in line, God (Castiel) thinks he's done rather well.
Many people have had to suffer, innocents, but he's averted the apocalypse until it's ready to happen without demonic (or angelic) assistance.
Before he's reabsorbed into his past self, Castiel (God) ensures his memories of the past several years will remain intact. There is no need to repeat past mistakes.