After upload Powerview file into SharePoint 2013 PowerPivit gallery, you could craete mutiple reports based on the file uploaded. We created two reports named "Report1" and "Report2" as in the following screenshot.
There will be multiple databases created to support Powerview reports on Microsoft Analysis Server as in the following screenshot.
We have also tried to delete the whole site collection completely as the following steps.
1. Delete the site collection from central admin
2. Run the command to remove the deleted site from queue
get-spdeletedsite -webapplication http://spsbx15 | Remove-SPDeletedSite
3. Run “Gradual Site Deletion” immediately to delete the sites that were marked for deletion
4. Delete the content DB from central admin
5. Delete the content DB from SQL server
6. IISRESET on SharePoint server
We are surprised that the multiple databases created on Microsoft Analysis Server are still there as in previous screenshot. The orphan database on SSRS database server is one of the Powerview issues that need to be addressed.
Added note on 8/21/2014.
After working with Microsoft support, we have identified similar issues published by Microsoft KB. After we upgrade our SSAS databases to 11.0.3412 which is 2012 SP1 CU9, this issue has been resolved. However, the trick is the orphan databases will be removed after we create another new Powerview report. It seems to me the new Powerview report creation will trigger to refresh the SSAS database.