What is really great about iCloud is that you can restore the missing files.
- Sign in to iCloud.com.
- Click Settings.
- Scroll down and under Advanced, click Restore Contacts or Restore Calendar.
- Click Restore the date before you deleted it.
- Click Restore again to confirm.
Tip: When you choose to restore iCloud content, you’ll see any available archives to pick from. A current archive will be made just in case you want to restore to the state where you are now.
Also note, that any shared calendars will need to be set up again as they are removed during the restore process.
Good luck :)