You can probably cancel with Ctrl+C, and it shouldn't be terrible. But really, you should not do anything further until you have a backup of all your important stuff.
Go check on Google how long hard drives last -- on average, it's barely 4 years. And like people and everything else, some die younger and some older. So it's not a matter of IF you will lose all your important files, it's WHEN. If you don't have a backup, it's already guaranteed to get lost forever, the only question is how long until that happens. On average, just a few years. Like the popular company likes to say, "you gotta back it up to get it back."