Have an option to select an item as 'discontinued from supplier'. This would allow in stock items to still show online, and in stock items to be sold in store, but would prevent out of stock items from being put on a work order at POS because they're not available any more.
Making a product inactive isn't the right solution, as that makes it unable to be sold, but what if we have remaining stock that we're clearing through but do not want to re-order other items in the matrix.
There is the option to mark a product as 'May not be placed on purchase order' but nothing at the POS if a cashier tries to sell a product that isn't available from a supplier.
This would be most helpful when there are several items within a matrix, some are in stock but none of them are available from the supplier