I don't know if the managers of the website can restore your tree. If not, then it's on you to take periodic backups of your tree. The best way to do that is to download/export your tree.
To do that, click the "download/export this tree..." button at the bottom of the sidebar, on the left. It will give you multiple choices for the format to export to; choose "Family Script", as it is the most likely among the choices to include EVERYTHING in your tree, AND be able to restore it all. On Windows, it will be downloaded/exported to your C:\Users\userID\Downloads folder and be named "My-Family-dd-Mmm-yyyy.txt" where userID is the ID you logged onto Windows with, dd = 2-digit date, Mmm = three char month name, and yyyy is the year.
How often you do this will determine how recently you can restore to (e.g. every hour or two, every couple of days, every month,...); how many of these you keep will determine how far back you can restore to.
