First try querying OBJECT_DEPENDENCIES - I've found direct queries more reliable than the studio's "Where Used" view.
Something like: SELECT * FROM OBJECT_DEPENDENCIES WHERE BASE_OBJECT_NAME LIKE '%your_pkg/AN_VIEW'
If anything returns, you'll see under DEPENDENT_OBJECT_NAME which objects are holding up deletion (also look at DEPENDENT_OBJECT_TYPE).
Sometimes I've seen HANA fail to drop lots of behind-the-scenes hierarchy views related to the model I'm trying to drop, so you have to drop those manually. You can use some crafty SQL against OBJECT_DEPENDENCIES to generate all of the drop statements for you, and then you just copy/paste the results back in the SQL editor and run them.
The next thing to try is looking at your Analytic Privileges. These won't be displayed in results from OBJECT_DEPENDENCIES. Manually open your APs and remove the model in question, re-activate, and then try dropping your model.
If both of these don't turn anything up - talk to your basis guy. I've encountered metadata corruption issues that are resolved by SYSTEM user taking over objects in question and dropping them with that user.