Hi nekkidmonk
If you want to separate inventories for any product, yes you could do so with Multi-Inventory.
So you can reserve some of your items for your online shop and leave the rest for the offline sales.
And, depending on how you want to configure this, you can choose between only allowing the online inventory's items on the WC side or continue getting items from the offline inventory (for any further online sale) once the online inventory is depleted.
Just to say that, probably, your POS plugin (if it's already changing the WC stock on its own), won't be able to read from any of the "additional" inventories you add to any product. Although, it should be able to read the WC inventory (that is the one we call "Main Inventory"). So if you always use the "Main Inventory" for your offline items, it could work I guess.
If you need more information about how everything works in Multi-Inventory, you can read [the documentation](https://forum.stockmanagementlabs.com/t/multi-inventory-documentation.
Best Regards,
Salva.