Wally didn't disintegrate.
He was sent to the American Heartland, his memory wiped from the blast. A farm took him, let him work on their land for room and board. As the weeks went by, he started to realize his superpowers pretty quickly. The family has been keeping this little piece of information on the downlow because they like this kid and his work ethic makes up for his insane appetite. His memory is still mostly shot, although he hears a woman's voice sometimes, sees these haunting grey eyes and he's pretty sure his name is Walman, which the family notes is kind of a strange name.
About seven months after Wally disappears, Artemis visits Conner at Kent farm because Ma and Pa think she's sweet. Pa takes her to the next town to get some feed and other supplies and she's happy to keep him company. She starts walking down the street window shopping while Pa does his business in the feed store. Out of the corner of her eye is this redhead. She's gotten so used to having her eyes play tricks on her every time a redheaded guy is near her that she refuses to look in his direction. Her eyes closed, she hears an older woman say, "You spoil me, dear," and her heart stops when a familiar voice responds, "Only for you, babe."
Her face snaps toward the voice, only to see the figure a good 100 feet away from her. He's tanner now and he has a beard, but—
"Wally?" she whispers. He doesn't hear her, and turns away to head to his truck. "Wally!" her voice croaks as she starts to move towards him, but he still doesn't turn around. Frustrated and sure she's going insane and it's his fault the idiot, she shouts, "Goddamn it, Wallman, LOOK AT ME!"
Walman turns to face the woman everyone else on the street thinks is obviously crazy, but some small part of his brain is screaming at him to pay her notice because he knows that voice. She shuffles awkwardly towards him, but he doesn't notice anything but her face. Her eyes. And like that experiment years ago, things snap into place.
"A—artemis?" his own voice wavers. Her oh so familiar smile shows up a second before he zooms to her side, picking her up in his arm and kissing her senseless. She starts smacking his arm even as they keep kissing.
"Don't you ever disappear on me again!" she gets out.
"Babe," he starts crying, "I—I didn't—" but his thought is cut off when he felt a push on his torso.
"Babe?" he looked in her eyes, "Why did your stomach just kick me?"