Hi Meghna,
You can run PP Production Planning with or without WM. The planning side is not related to how the inventory is managed.
If you will not have WM you can use the Stock Determination and the Pull List.
You can read about this here:
Pull List - Repetitive Manufacturing (PP-REM) - SAP Library
Stock Determination - Inventory Management and Physical Inventory (MM-IM) - SAP Library
Hope this helps.
Kind Regards,
Mariano