Some people have told me to write one where GLaDOS doesn't pull Chell in at the end. I won't write that because there is a fan fiction on deviant art called "Won't Let You Go" by PsychoColette that does a much better job of it than I could.
Alternative getting the portal gun
Chell looked out the broken glass on test chamber two. There wasn't a portal gun. How would she complete that test? She walked into the room to try to figure something out.
"Hey you made it. There should be a portal gun on that podium over there, can't see it though." Wheatley said when he saw her. He slid on his management rail so that he could see her better. Chell was thrilled to see him. He had helped her so far, why would he stop now?
She stared in the direction he was motioning her to. There was nothing there. "Maybe it fell off?" He said. Chell walked towards it. The floor gave under her. She hit her head hard on the floor as she fell. "Did you find the portal gun? Also, are you alive? Should have asked that first." Wheatley's voice came from above. Chell was lying in the water face down, unconscious.
"I'm going to work on the assumption that you're still alive and wait for you up ahead. I'll wait one hour then assuming I can locate your dead body, I'll bury you." He continued to talk as Chell drowned.
Wheatley came back one hour later after finding a way down to where she was. "Look what you've done Wheatley. You killed her. The last live test subject and you killed her." He told himself. Then he tried to bury her the best he could by throwing some plants on her. "She was another smelly human." He said as he left.