Contact Support with the details. You should be keeping your own offsite backups, so hopefully you did. If you were on an old server, you may have a ~/.snapshot directory you can check via shell or SFTP. You can also go to the Web Panel and go to Domains -> Manage Domains. In the right most column for the domain should be a "Restore" link you can click on. But again note the disclaimer at the top: "We make NO GUARANTEES about keeping backups of your data!
You should ALWAYS keep your own off-DreamHost backups of all important data!"
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