Hello,
The information in your Active Listing tab will be updated when Auctiva synchronizes with ebay. I suppose you could delete the listing on Acutiva by deleting it from anywhere it is saved, such as your Saved Listings, Active Listings, etc. That might get it out of the scrolling bar sooner. Not absolutely positive, however.
If the item has been ended on ebay, its ended and a customer wouldn't be able to buy or bid on it. So no worries there.
Hope this helps.