Websites can go offline or get hacked a number of different ways. If a server fails then you could lose your whole website or it could end up being offline for days until the hosting company has fixed the problem.
The best way to get you out of a mess like that is by having backups of your website files and database. Backup WordPress does this for you can schedule backs of the database daily and the files either daily, weekly or monthly. It also allows you to download a zip file to your local computer. This will allow you to upload the website to another server while the problems are fixed on the original server or revert the website back to a previous date in case the website was hacked.
Save yourself the stress and damage to your business by having an up to date backup available and know how to use it quickly.