Pages, Parts and Templates:

Version 6.45 and lower:  Parts, pages, and templates cannot be individually restored. The only way to restore one of these items is to restore the entire NetCommunity database to a point in time when the affected items are known to have existed as-desired. Blackbaud also highly advises that if a restore of a NetCommunity website is performed, that the Raiser's Edge and Education Edge (if used) databases also be restored to matching points in time to ensure data integrity.

Version 6.45 and above: Parts, pages, and templates can be individually restored in NetCommunity under Site Explorer. 
  1. Select either Pages and Templates or Parts.
  2. Click the Deleted Parts or Deleted Pages/Templates folder under the Folders tab. 
  3. Mark the checkbox in the Action column for the row that corresponds to the Page, Template, or Part that you wish to restore.
  4. Click Restore.
Note: Fundraising Personal Pages, which are deleted cannot be restored. The fundraiser would need to create a new page.

Layouts/Style Sheets

As site layouts are designed directly using HTML, there is not a restore option. 

Additional Resources
Is it possible to restore a deleted email message?
How to restore a deleted file or file url
How to Restore a Deleted Form