If you deactivate a project in SCTM and then delete it, are all of the assets related to the project deleted or are they in an "obsolete" state?
If a project has been deleted then all related assets are deleted (e.g. requirements, tests, results, reports). This can be confirmed when reviewing the application server log.
When a project is deleted they are not deleted immediately. The deleted jobs are put into a job queue; therefore this is not started immediately. If the deletion of the project fails, then the projects are not deleted but set to archive which would not be visible in the UI.
The only information which would remain would be the x-project related assets (versions, builds) remain.