No, this story doesn't have a happy ending. It is a sad story of teenage boys whose mission is to destroy an innocent man's home for no reason other than it is still standing in the town that has been destroyed by World War II bombing. The boys carefully plan how to destroy the house and do so over a couple of days, methodically and meticulously. At the end of the story, a truck driver starts his truck and hears a crash behind him as he pulls off. He doesn't realize that his truck has been tied to a main beam in the home and that he brought the entire home crashing to the ground until he steps out of his truck to look at it. Mr. Thomas (the homeowner) is devastated when he sees it, but the truck driver laughs at the situation, which adds to the sadness and sheer meanness of what the boys did.
techinically speaking its a happy ending because the definition of a happy ending is that the it ends to the protagonists favour, or something like that. although the ending may seem sad, with the house and Mr. Thomas's future, the point of view of the story can make Mr. Thomas look like a antagonist, and thus an ending that does not end for the antagonist favourably, it is a hapy ending.