Hi Mathew,
Proceed with the deleting when all users are out of the system.
Fisrt of all perform a Hana full backup.
Then:
- go to Control Center site and stop the Enablement (if you set it);
- cleanup this schema export files on Hana server export directory (if you export this specific schema);
- cleanup the backups performed from Control Center (if you have it);
- On Hana Management Studio, right click over the database and delete it.
It is common, when you start B1 the first time after the deletion, the database remain in the selection list as a valid company to connect. Simple click over the [Refresh] button on the logon screen and it will disappear.
This is the procedure I usually do. If you are not confident, you can test in on a test or development environment first.