There are likely to be some holes in continuity regarding the time differences between wherever Clint lives, and Wakanda, but I just used my imagination.
Clint Barton sat on the front porch, swinging gently back and forth on the swing chair that faced outwards, towards the sunset. It was early evening, and there was a faint breeze that hung about, gently moving past the obstacles of the Earth. Inside, he could hear Laura preparing for dinner, talking quietly to Lila. Cooper was upstairs, minding Nathaniel. The boy had become extremely protective of his younger brother, which was a good thing, and Clint had feared that he may have become sullen and jealous of the presence of a younger sibling.
Clint knew something serious was happening. Nat had contacted him earlier in the day with a message simply stating, "Stay at the farm." Clint was itching to find out what it was, but he knew he needed to stay with his family. The days of fighting with the Avengers was over; they had broken up anyway, like some kind of dysfunctional 90s boy band. And yet Clint found his mind wandering to the storage unit under the barn, where he stored all his weaponry from his fighting days. He wondered if he should move them into the house; if whatever was happening truly was serious, maybe it was a safer idea…? Clint shook his head. No, he and Laura had agreed to having no weapons in the house, especially while the kids were so young. He should be safe here anyway, they all should be; there were no records of the Barton family being anyone other than Clint himself. Sure, what had been the Avengers knew about them, but Clint knew…hoped…that they would not share such precious information to anyone. They would be safe, no matter what. Clint took a deep breath and leaned back in the chair; he had been leaning forward, with his shoulders tensed, without even realising it. He stared out across the farm. It truly was a good life, the family life.
A sharp clatter came suddenly from the kitchen, followed by a gutwrenching scream. It was Laura. Clint bolted from the swing chair and tore through to the kitchen. Laura was standing at the bench, carrots thrown aside, her hands grasping at Lila. Clint froze. His daughter was fading away, peeling into nothingness, flaking away like leaves in the gentle breeze outside. Clint ran forward, but by the time he reached Lila, she was nearly gone. She turned her head to him, her eyes wide and swimming with frightened tears, "Daddy?". And then her face dissolved, and all that was left was a pile of wafting dust. All Clint could do was stare. Laura was silent as well, an awful, pained expression of horror on her face. Then, she seemed to rouse herself somewhat.
"Cooper!" she called for their eldest child, a slight hint of fear in her voice. Clint and Laura turned their heads to the stairs. There was a moments silence. And then,
"Mum?" he didn't sound panicked. He must have had his headphones on again. And then, there was a scream from upstairs.
Clint reached the staircase first; he sprinted up them, not looking behind him, though he could hear Laura close on his heels. They reached the landing, and crossed the floor to the playroom door, where Cooper had been playing with Nathaniel. Except, Cooper wasn't there. A pile of dust lay on the floor, next to where Nathaniel lay, kicking his feet in the air, unaware of any distress. Clint leant on the doorway in horror as Laura pushed past him, screaming for her son. She lifted a pile of the dust up in her hands and cradled them closely to her chest. She was crying hysterically. Clint stared at the scene, trying frantically to make sense of it all. His daughter and eldest son lay in a pile of dust at two points in the house, his wife was inconsolable on the play mat, and their baby was rolling around on the ground. At the sound of his mother screaming and crying in distress, Nathaniel began to cry. Instinctively, Clint moved forward to pick him up, and then he froze again. Laura was dissolving before his eyes.
"Laura!" he screamed, dropping to his knees beside her. She looked at him, and placed a hand on his cheek as he stared at her rapidly dissolving face in horror, tears forming in his eyes.
"I love you." She said to him, breathing rapidly.
"No, don't talk like that, it's gonna be okay, I promise you, I-"
And then, she had dissolved, and Clint was left clutching a pile of dust. He didn't know what to do. He felt blank. He dropped to the ground, bringing his knees to his chest, deaf to the sound of Nathaniel screaming. He sat like that for a period of time, before he suddenly seemed to snap back to reality in some way. In an almost robotic movement, he scooped up his son in his arms, and left the playroom. Out on the landing, he paused, staring down the stairs at the remains of his daughter, now nearly completely blown away by the breeze that had now become a wind that moved through the door Clint had left open in his rush. He blinked, and quickly walked to the room that he shared with Laura. He placed Nathaniel in the crib, and then, after pausing for a moment, picked him up again, not wanting to lose the feeling of holding his seemingly only remaining family in his arms. Nathaniel had suddenly stopped crying, and instead stared up at his father. Clint stared back, and Nathaniel gave him and gummy smile, and hiccupped. Clint chuckled slightly, and then screamed; he felt the solidity of his son changing, and the same, flake-like dust began falling to the ground. Nathaniel looked at his father, still smiling – he didn't seem to feel any pain.
"I'm going to find you, my boy, all of you, mummy, and your brother and sister, I'm going to get you back, I- "
Nathaniel dissolved.
Clint sank down onto the wooden floor next to his bed. Grief, loneliness, confusion, anger, overwhelmed him. He screamed into nothing, clutching at his hair, tears pouring down his face. His family, his whole family, was gone. Just like that, in a cloud of dust. He couldn't comprehend it. He was alone, no one was around for miles. He reached up mindlessly, and grabbed the old cell phone that he used to communicate with Natasha. He flipped it open, dialled the last contact, and put the phone to his ear. It rang for a few seconds, and then, the call was picked up.
"Clint? I can't really talk right now, something big has happened." Nat sounded exhausted, and there was a tone of immense sadness in her voice.
"Nat – "
"Clint, really, I'll call you back – "
"They're gone. They're all gone." Said Clint abruptly. There was silence on the other end of the line.
"…Who?"
"Laura, Lila, Cooper, and Nathaniel. Nat…my whole family just dissolved in front of me. They're gone." There was more silence on Natasha's end. Then, Clint heard something he had rarely heard before; Nat was crying.
"Clint, I'm sorry. I should have told you what was happening. They're gone, Clint, they aren't coming back."