Children are amazingly resilient, and tend to bounce back from situations pretty quickly. Anita Desai did a good job of capturing the despair that Ravi felt; such dramatic tragedy felt by the small child captures the intensity of those childhood emotions where it feels like the entire world is crumbling around you. Even though that moment that Ravi felt left out, and "crushed" by his own "sense of insignificance" was truly horrible for him, I believe that he will recover. As soon as one of the other children notices him, and says hello, or asks him to join in, he will be over it. However, your question asks if that lesson, that he isn't as important as he thought he was, will remain strong. I don't know if that lesson will remain strong , but I definitely think that he will remember it. How else do we grow up, but through life teaching us valuable lessons about ourselves and our place in the world? This lesson is one that Ravi will keep in the back of his mind, and add it to his overall knowledge about himself, which will in turn aid in his maturity. Slowly, children lose their naivety and innocence, through experiences just like this one. So, even though it might not "remain strong" with him, it will stay with him, and add to the other experiences that will eventually turn him from a child into an adult.
I hope that those thoughts help to you get you thinking. Good luck!