Tonsils are an important part of our immune system. They capture the germs entering the body. When they get infected, doctors prescribe antibiotics. If the infection does not response to the medicines then it becomes necessary to excise them.
You can always get second opinion for surgical cases. Tonsils will not grow again. There is a very very rare condition that a part of tonsil tissue may regenerate but it will never re-grow to the original size and cause any harm.