Hi!
You can delete your old listings on Auctiva and it will not effect anything on eBay. However, when you delete images on Auctiva, your closed eBay listings will show a red "x" where the images should have been. By default, we automatically save deleted images for 7 days (just in case you delete one by mistake--you can restore them) and after 7 days they will be gone from your eBay listings. There is an option when deleting images on Auctiva to delete them immediately for good, in which case your images on old eBay listings would show an "x" right away.
Hope that info helps! Good luck!