The user creates a map and doesn't provide access to other users. 

When this user who is diagram owner leaves the organization or he is no more be a part of Tibco Nimbus and Administrators will remove the user's account from Tibco Nimbus. 

Due to this, no other user including administrators in the Tibco Nimbus will be able to access the diagram created by this user.

If the user who creates a diagram only can access the diagram and in the future when the user will not be part of Tibco nimbus, other users will not be able to access that diagram. In this case, the customer has to contact Tibco Nimbus support and they will explicitly provide access to the Tibco Nimbus for requested users.

To avoid such a situation, the user can follow the below steps,

--> Create a group from Tools --> User Accounts --> New Group 
     For Example, the Authors or Administrators group can access the diagram.
--> Open Author Client
--> Go to Administration -> System Options -> Default Access Rights
--> Click New Map tab
--> Select appropriate Access Rights
--> Add user or group which requires default access right to every newly created map.
    Note: To enable the above option, the option "Default new maps to private access" should be disabled. you can select access denied in the New Map tab which is the same as this feature.
 
Whenever you create a new map, the above default access right setting will be enabled for that map and the group which we created will be added in the diagram access rights automatically.
When a user will be deleted from the Tibco Nimbus, the users who have added as above can access the the respective diagram.