Oh dear. First off, don't panic. Not all is lost. You have a few options:
i) Raise a support ticket and ask us to restore the site from a backup. This usually takes around two hours. NB: you need to be quick, though, as the backups are taken once a day, so we can only restore sites you've deleted today or the previous day. Due to the nature of the work involved, we would normally need to charge for this work, however.
ii) Re-create the site on the system and if it's urgent (for example, you need to run a report for a client) raise a support ticket and us to prioritize the jobs for this site (primarily: keyword ranks, spidering, link imports and GA imports). You can now also backdate GA data imports when you re-configure Google Analytics access, so if you've lost historic GA data, pushing the start date for the import back will restore this data. (If your site was configured for Omniture (Adobe Site Catalyst), you will need to let us know when you raise a ticket how far you'd like us to go back and we'll see if we can restore the Omniture analytics data).
What have you lost?
Potentially the most annoying loss is historic ranking data. We obviously can't go back in time and work out what your rankings for this site would have been on a particular date for a particular keyword. However, if you have records (ideally in Excel) of keyword ranking histories exported from our platform, you could ask if we could re-import that data back into the platform. You would need to raise a support ticket, copy the data to a keyword history Import template file we can send you and email us that completed file. We could potentially then restore your historic ranking data.
Sites can always be re-spidered. Link data is stored by Majestic SEO, so can be re-imported and we don't typically lose historical numbers.