I wouldn't be so sure. If she wins tonight, her emails and all the other stuff people criticize her about will be faded memories in 2020 and she will be judged by her performance as president. So if she keeps the country safe over the next four years and the economy keeps improving, it will be difficult to make the case that she needs to be replaced. No president has lost reelection since 1992 for that reason.
People don't automatically die in their 70's. Jimmy Carter, George H.W. Bush, and Bill Clinton are all still alive and they're all older than both candidates. Presidents usually get the best healthcare money can buy, so I don't expect anything to happen to whoever wins.