I found a go-around way of fixing this problem which I myself foolishly did (not unmapping the image from the item before deleting the product.) For those of you who have already deleted the demo products, simply install abantecart again to your public_htm folder under a different folder so as not to disrupt your previous updates. Login. Go to the Data tab. Export the demo product lists. import it back to your original abantecart (the one you've been updating) and voila, now you have your original "demo products" back. From here you can start unmapping the images from the product and delete the corresponding images.

Hope this helps! I purposely made an account just to share my victory!