everything has been deleted

Regular backups (daily at a minimum) would allow you to restore your site from the backup. You can ask your web host if they do periodic backups, and if so they might be able to restore it for you. Going forward it is a good idea to maintain regular backups on your own or through any number of backup plugins or services available.
Check out these articles:
https://codex.www.ads-software.com/WordPress_Backups
https://codex.www.ads-software.com/Backing_Up_Your_Database
Or a simple to use plugin: https://www.ads-software.com/plugins/wordpress-backup-to-dropbox/
You might be able to see if the host keeps logs of who accessed your site, but they may only be able to produce an IP address at best – it won’t tell them specifically who did something to your site though.