Database which can be setup without admin user I'm looking for a database (relational would be preferred, but NoSQL is also okay) which can be run without an admin user. I want to setup the database with an admin user, but then delete the admin user forever and run the database only with non-admin users. 
Is there anything like that for Postgres, MongoDB, MySQL, etc.?

EDIT: The goal is to make the database 100% safe from unrestricted deletions. The normal users should only be able to insert data, deletions and edits should never be possible, also not for the admin.

Thanks for the help!
The reason you have Superusers is to clean up the mess made by regular Users. 

Trying to take these powers away from Superusers is like asking them to service your car and promptly throwing away all their spanners and wrenches. 

You say that you don't want data deleted.  

Simple solution.
Don't give people the permission to do delete data. 

Argument: "But Table owners can do anything to that table"  

True.  So don't give Users table-owner-level accounts. 

Argument: "Superusers can do anything" 

True.  So don't give Users superuser-level accounts.  

Only you should have access to this, to fix other people's messes.  

Review your security model.  Determine who needs what level of access to what, then apply it.  You may well get some "resistance" to start with, but stick to your convictions.  You're heading in the right direction.