From To Kill a Mockingbird, how would I write a short script based on "Scout Walks Boo Home," but she never saw him again due to his shyness and childlike behavior?

If one were to write a short script about Scout walking Boo home on the night that he saves her life, it would certainly be one-sided because he doesn't speak. Scout, therefore, would have all of the lines, and she would have to verbally interpret Boo's body language for the audience to understand. Within the script, then, stage directions might be useful to indicate Boo's part. For example, some ways to describe Boo's movements could be as follows:

"When Boo Radley shuffled to his feet, . . . every move he made was uncertain, as if he were not sure his hands and feet could make proper contact with the things he touched. He coughed his dreadful raling cough, and was so shaken he had to sit down again. His hand searched for his hip pocket, and he pulled out a handkerchief. He coughed into it, then he wiped his forehead . . . His hand tightened on mine and he indicated that he wanted to leave" (277-278).

From the passage above, examine Boo's mannerisms and body language, then apply those into the script. Scout even says that the way Boo communicates is through "his body English," which she could mention in the script as well. 
As far as what Scout might say on the way to Boo's house, she might say a few things in the script that she wished to say from the novel. For example, Scout feels as though she and her family haven't been as neighborly as they could have been as expressed in the following excerpt:

"Neighbors bring food with death and flowers with sickness and little things in between. Boo was our neighbor. He gave us two soap dolls, a broken watch and chain, a pair of good-luck pennies, and our lives. But neighbors give in return. We never put back into the tree what we took out of it: we had given him nothing, and it made me sad" (278).

Maybe at the end of the script Scout could mention that she will suggest to Atticus to send Boo Radley a gift for helping them out that night. Or maybe Scout promises to tell Jem everything when he's awake in the morning, too. Whatever Scout says, she does know that she most likely will never see Boo again. However, she would rather respect his wishes than annoy him by trying to get him to communicate if he doesn't want to.