That's the last medical checkup on legal and humanitarian grounds. If the doctor certified that the condemned man is going to die anyway within 3 months, a presidential clemency may be appealed for to let him die naturally. However, I've never heard of any doctor daring to do that. Hang once until death, that's the legal sentence. If the condemned man got off the noose alive, that's the end of the legal case. He walks away a free man. However, I've also never heard of such a happenstance before. The hangman must make sure that the condemned man dies in one hanging.