For those who have seen the pics for Avengers 4, a short ficlet based off one of the tiny details...
For those who have not but don't care about being slightly spoiled, a little ficlet based various discussions and conjecture, not known facts...
For those who don't want to be spoiled in any way at all... STAY AWAY.

They were finishing up their lunch at the little dive diner Clint had picked when a sudden and shocking feeling came over Natasha, like someone had snapped their fingers and wiped out half of humanity.

"Hey, you ok?" Clint asked with concern.

"I don't know," she answered slowly, trying to shake off the feeling. "I just felt... " She shook her head and smiled at him in embarrassment. "Never mind. It's ridiculous."

"Try me," he said, snagging a piece of her pie.

It was a sign of how rattled she was that she didn't protest or try to stab him with her fork. Instead, she sat back and fiddled nervously with her necklace a little before leaning in closer and asking, "Do you ever feel like there are different timelines out there?"

He looked surprised, but answered her seriously. "You mean like multiple dimensions? Or Timey-wimey, wibbly-wobbly stuff?"

Natasha raised an eyebrow at him.

"What can I say? Tony likes to binge watch Doctor Who and sometimes he gets me sucked into watching late at night." Her eyebrow rose higher and he shrugged. "What? It's good!"

She hummed softly at that and then thought about what he'd said. What did she mean?

"Multiple dimensions," she finally answered. "Like what if you hadn't divorced Bobbi? Or I'd stayed with the Red Room? Or… I don't know, if I'd started dating Bruce?"

Clint snorted. "Would never happen."

"Clint."

He sobered. "Ok, it's possible, but ridiculous. Like suggesting I have a secret farmhouse hidden away somewhere with a pack of kids and some faceless wife."

She smiled at that. Clint with a wife and kids was a ridiculous notion. Still, the idea niggled at her and she fiddled with her necklace some more. "But what if those things did happen? Some time -- or some where -- else?"

"So? You just said it. Another time, another place. It wouldn't be us. At least, not this us," he said, scooping up her last bite of pie.
"But what if other things happened? So that we weren't this us?"

He reached across the table and took her hand in his. "Nat, listen, I know that things are weird sometimes, but we are this us. Can't change that." He glanced at the door. "What we can change is whether we're going to be late meeting Cap or not. What time did he say?"

"One," Natasha answered, happy to have something solid to focus on, something grounded in reality. "At the armory."

Clint slapped a couple bills down on the table. "Then let's get going.