Consider the following things are already satisfied.
1. The maria-db is running in separate pod and is pre-installed.
2. When we deploy a new service it is able to connect to maria-db and create SCHEMA in it.
But the final requirement is when the service is deleted then it should cleanup the SCHEMA. I have tried writing a job with post-delete tag.
So just a thought, you could possible do this by using a Admission Control i.e your logic could possible be along the lines of:
Delete Pod Requested --> Hits Addmission Control --> Addmission Controller Removes Schema --> Pod Deleted
However this would be a lot of custom code and you would need a way to identify the Schema that that particular service has created in the DB.