I come across many issues with business ownwers because they never thought about backup files of their website, or worse yet their previous web designer didn't have a backup before something went wrong. This leaves the business owner with nothing but a memory of a website. Many things can go wrong when it comes to your website and keeping a copy of those files can prevent a world of pain. Make sure your web designer keeps weekly backups of your site at a minimum. They should also keep multiple copies and keep a copy in more than one location.
If a hosing company has a natural disaster or goes out of business you can lose your data. Your web designer can also lose files due to storms, fire, etc. An ounce of prevention is worth a pound of cure. If you buy your website you should ask for a copy of the webfiles. Whenever changes are made get a copy or make sure your web designer has a copy stored in case something goes wrong. If you have a fallout with your website company you still have you website if you have a copy of the files.