I found this article on tonsil regrowth:
if even a small bud of tonsil or adenoid tissue is left behind by the surgeon, the tonsil or adenoid may regrow. With regard to tonsillectomy, the risk of regrowth depends greatly on technique. At one time, some surgeons performed subcapsular tonsillectomies, in which the outermost shell of the tonsil was left behind. I am told this operation was less painful than a regular tonsillectomy, in which the entire tonsil is removed. Unfortunately, incompletely removed tonsils have a nasty tendency to regenerate. this is from:
are you personally concerned about this? I would agree that if the tonsil grew back, espeicially if it were to grow back from some infected tissue that hadnt been removed, it is could seriously be possible. Im sure it would be an unlikely situation though.