I'll add a couple of things to @katescott's helpful post on backing up.
Get familiar with search engines ( Google, Bing, and etc. ) and their page cache mechanisms. While not a backup of your site, those caches can sometimes help you recover some of your content. You have to do it fast after you notice the loss or the cache may not have the content anymore.
Also check the Wayback Machine. Again, not a backup but you might find some of the content there.
The site duplicate feature is the closest thing to a backup although you can't automatically move content from the duplicate back to the original. The duplicate is still on SS's servers. In the very unlikely event that SS had some kind of huge disaster, one could lose everything.
If you want the content locally there is an old school command line tool called wget that may be of use. Wget is a very complex tool but should be able to capture the basic content of your site.
What happened? Who deleted it?
Squarespace doesn't have a user backup option, and exporting as wordpress doesn't have a huge utility.
Have a read of this: https://www.katescott.co/blog/how-to-backup-your-squarespace-website
katescott reacted to creedon in How do I backup my website, after unlikely event of Squarespace deleting my content?
