Since we sync your inventory information directly from Amazon, if you delete your listings from Seller Central, they will be removed from the Inventory page in InventoryLab. It will not remove information from the Accounting pages or reports containing the item.
Note: If you simply 'Close' the listing (remove the item from sale), it will still appear in InventoryLab.
Before you delete anything, be sure to enter any missing accounting information such as supplier and buy cost on your Inventory pages. This ensures that data will be captured for past sales and subsequently filter it into your P&L Report, along with the other reports.
If you happened to delete items before entering this info on the Inventory pages, no worries! You can update this in the Sales page manually for each sale or via import.