AU: They lived:
Sirius knocked James to the ground as he barreled into him. He felt his best friend let out a sound of surprise, but he didn't care.
"You're alive!" Sirius practically yelled. "You're fucking alive!" James patted his back, and shifted a little under him. Sirius sat up, and James fixed his glasses, getting up with a small smile on his face.
"Yeah." He said in a weak voice. "I don't know how, but we're both alive." It had seemed impossible, but Sirius' grin grew even wider.
"Lily?" He called, getting up. She appeared in the doorway and he enveloped her in a hug, picking her up and swinging her around in glee.
"You both survived!" He said. His voice broke a little then, and he quickly wiped his eyes. "I'm so happy you both lived."
Lily nodded tiredly, and James put an arm around her shoulders.
"I don't know what I would have done without you." Sirius said mournfully. James shook his head.
"Lucky for you, you don't even have to imagine it."
"Sirius?" Lily said in a small voice. "Last night's battle was widespread and all of the Order members on patrol were posted in different areas-"
"Did you find out where she is?" Sirius interrupted in a tense tone. Lily nodded, biting her lower lip nervously.
"Yes, but I - I don't know if she made it." Sirius felt a sharp pang of pain in his chest, but he shook his head resolutely.
"She did. She had to." He said definitively.
o-O-o
The dizziness stopped and for the second time that day, Sirius opened his eyes to a scene of ruin. He felt dread seize his stomach and he forced himself to breathe. Many impossible things had happened in the past few hours. If James and Lily could survive, and Voldemort could be defeated…Marlene could live. She did.
He walked towards the abandoned warehouse - now just a series of standing doorways and walls - where the majority of the fighting had taken place. The fear threatened to paralyse his limbs but he forced himself to keep walking. He had to see her. He had to know.
His heart almost stopped when he saw her leaning against a wall, struggling to get into a more comfortable position. Her hair was dirty and matted with blood, and the way she winced with pain wasn't reassuring. But she was moving. She was breathing. She'd lived.
He ran towards her, falling to his knees and taking her into his arms before he could even catch his breath. He felt her sigh and weakly hold him back before he brought her face up to his and kissed her for all was worth. He broke away eventually and began to kiss her eyelids, her cheeks, her lips, her nose, her forehead, everywhere he could.
"I can't fucking believe you lived." He said in a disbelieving tone, holding her close again. He felt her fingers curl loosely into his shirt.
"Me neither." She said in a thin voice.
"I thought I - I was so scared-"
"Shh." She said soothingly. "It's over. We lived."