Here's the ending of the radio version:
Narrator: The night George saw his uncle off he walked homeward slowly through what appeared to be strange streets in a strange city, for the town was growing and changing as it had never grown and changed before. It was heaving up in the middle incredibly, and as it heaved and spread it befouled itself and darkened its sky. From day to day, from week to week, great new industries were springing up, steel and oil, and this new all-conquering thing, the automobile.
Strange people swarmed about him obliterating, destroying every trace of the magnificence that once was Amberson, destroying with it the last of the Ambersons, George Amberson Minafer. The city rolled over his heart and buried it, as the city had rolled over Ambersons and buried them to the last vestige. A thing had happened, the thing which years ago had been the eagerest hope of many. The hope of many good citizens had finally come to pass, but not one of them was there to see it. George Amberson Minafer got his comeuppance. He got it three-times filled and running over.
Later, as he walked down Amberson Boulevard, now known as Tenth Street and filled with second-rate shops and cheap boarding houses, and climbed the stairs of the old house for the last time, a terrible loneliness assailed him. He opened the door, softly, into Isabel's room. It was still as it had been. Tomorrow everything would be gone, and soon after that the very space which tonight was still her room would be cut into new shapes by new walls and floors and ceilings.
Yet, Isabel's room would always live, for it couldn't die out of George's memory, and whatever remained of that old high-handed arrogance was still within him, he did penance for his deepest sins that night, and it may be to this day, some impressionable, over-worked woman in a kitchenette, after turning out the light, will seem to see a young man kneeling in the darkness, clutching at the covers of a shadowy bed, and it may seem to her that she hears a faint cry, over and over...
George: Mother. Mother, forgive me. Mother? Mother. Forgive me.
Narrator: You must have guessed by now who George Amberson Minafer was. Take my word for it, please, that the George Amberson Minafer who was, is no more.
Eugene: Why Lucy! What brings you downtown this morning?
Lucy: I tried to get you at one of the factories, but no one could locate you. I wanted to talk to you, Poppa. Are you very busy?
Eugene: I'm never too busy to talk to you, Lucy. Is something wrong?
Lucy: Yes, Poppa, there is something wrong. It's George.
Eugene: George? You mean...
Lucy: Yes, Poppa, George Minafer.
Lucy: He's been hurt, badly hurt. He's in the city hospital, both his legs broken.
Eugene: That's too bad.
Lucy: He was run down by an automobile.
Eugene: An automobile? George Amberson Minafer run down by an automobile.
Lucy: Poppa, do you know what he's been doing the past two years?
Eugene: No, no, and I couldn't honestly say, Lucy, that I'm very interested.
Lucy: He's been working with explosives at the Akers Chemical Company, a dangerous job, the most dangerous job there is.
Eugene: Well, I never thought he lacked nerve, Lucy.
Lucy: You don't understand, Poppa. No one else would take the job. He needed work so badly he took it, and... and Poppa, he's made good. He's changed. He's not the old George at all, and now this has happened to him.
Lucy: I want you to go to see him.
Eugene: No, Lucy. After all, you can't expect me to have any particular affection for that young man.
Lucy: I'm sure that Isabel...
Eugene: Isabel... Isabel's been dead three years... three years... and if it hadn't been for him, she might... she might -
Lucy: It's what she would want you to do, Poppa. You know that. She'd want you to be kind. She'd want you to come with me to the hospital. He's lonely, Poppa. His heart's broken. He needs us. We can help him. You could do so much for him, and I... I could... Well, Poppa, what are you going to do?
Eugene: Isabel, my dear, up there in that small, bare hospital room this afternoon, you were by my side. Do you remember, Isabel, that last day we were together? You said that things in our lives were like smoke, and time like the sky into which the smoke vanishes, and I told you that, for us, things would not change like that, that we would always be together. You were with me when I walked into that room where your son was lying, with Lucy sitting beside him. He felt you too. He lifted his hand in a queer gesture, half forbidding, half imploring. "You've come," he said, "you must have felt my mother wanted you to come, so that I could ask you to forgive me." And as he held my hand in his... if you could have seen Lucy's face at that moment, dear Isabel, she was radiant, but for me another radiance filled the room... for then I knew that I had been true to you at last, my true love, and that through me, you had brought your boy under shelter again.