What happened after Bruno went missing?

Nothing more was ever heard of Bruno after that.  Soldiers went around the whole Out-With to look for Bruno. But only Bruno’s clothes were found on the fence. Mother didn’t return to Berlin quite as quickly as she hoped. She stay at Out-With, she thought he might have made his way home alone. She immediately returned to their old house, half expecting to see him on the doorstep waiting for her. He wasn’t there. Gretel returned to Berlin with Mother and cried a lot because she misses Bruno so much.  Father stayed out at Out-With for another year waiting for Bruno. He thinks about Bruno day and night.

One day, Father formed a theory about what might have occurred and he went back to the fence where the pile of clothes had been found a year before. He discovered that the base of the fence here was not properly attached to the ground as it was everywhere else and that, when lifted, it left gap large enough for a small person (such a little boy) to crawl underneath. As he followed through it logically, when he found that his legs seemed to stop working right and he fell right down the floor.

That’s the end of the story of Bruno and his family.

Why this ending is a good or a bad one?

I think this ending was a bad one because the ending was a sad ending. Bruno died in the end, his parents and his sisters were upset about his missing.  If I was the author, I would write the ending as Bruno being brought to a faraway country to works. And his father managed to follow his theory and find Bruno in the end. Bruno and his family left happily ever after.