What did Ponyboy decide to do after he read Johnny`s message? Why did he decide to do this?

Ponyboy realizes that Dally has died because he let his gold fade, but that it doesn't have to be that way for all the Greasers and disadvantaged people.

So Ponyboy calls Mr. Syme, his English teacher, and asks if his theme can be longer than five pages. When he gets permission, he begins to think about how to start the story, and decides to begin with "When I stepped out into the bright sunlight from the darkness of the movie house, I had only two things on my mind: Paul Newman and a ride home..." which is the opening of The Outsiders itself.

He acts as if nothing happened