It should never be possible to delete the Default Permission Scheme.

The reason for this is that a project cannot be created without a Permission Scheme.

So if the Default Permission Scheme is not used, and the Bulk Delete Scheme Tool is used to delete the Default Permission Scheme, then all projects and all other permission schemes are deleted, it will not be possible to create a new project. A new permission scheme would need to be created before creating a new project.

The above scenario is unlikely, but we should still fix this problem.