Does trauma to the testicles causing hernia, and surgical removal, always leave behind a hematocele resembling testicular cancer that lasts many years?

Testes Trauma. Not at all. The hematocoele is a collection of blood which will eventually be re absorbed. In the meantime, it presents as a firm mass that mimics a tumor. It should shrink and go away; if not follow up with your doctor.
No, and no. Testicular trauma does not cause a hernia. While it is possible to have bleeding postoperatively that results in a hematocele thatch last for years, this does not happen in every case, nor does it mean the case was botched. It is most likely an unavoidable side effect if the operation.