yes, it is certainly possible that portions of the copper are still in the tank as copper metal surrounded by a thin oxidized layer. generally, the corrosion would utilize a weak spot in the wire and break it, while only surficially oxidizing stronger portions - and those may still be in the tank. based on that, i would recommend running a poly-filter (or cuprisorb, as paul mentioned) for an extended period of time - say 6 months or so in order to give any potential copper pieces time to oxidize completely and to catch any copper ions that may have dissolved during that time period.
paul makes a good point as well - the change in the corals is probably due to the electricity pumping through the tank. however, if the corals haven't shown real signs of death at this point, they'll likely be fine with good husbandry. in fact, some places pump low voltage electricity through piping in manmade reefs as a way to enhance coral growth - you may have gotten lucky with the amount of current going through the tank that it wasn't strong enough to kill the corals. http://www.wired.com/science/discoveries/news/2004/08/64671