You can still make backups on all platforms. So it would be a matter of restoring a backup. Typically someone with local vaults also syncs (to either iCloud or Dropbox) so in theory as long as they still have access to that account they can sign in and access their 1Password data. I'd still suggest backups in addition to that, a sync file is constantly changing, and is not an actual backup.
Hope that helps though!
Kyle
1Password Security Team