I feel for you as we are all animal lovers and hate to see a death. Animals die in our care and as long as we learn and try not to do it again it's okay. Remember that a fish, almost any fish will eat another fish that is smaller then it and can fit it in it's mouth. Stress is the #1 killer of AQ fish and you must be leary of adding any fish with a lion fish in your tank. Raise your SG
and do a few more PWC
's and you should be okay. Don't beat yourself up on this event because as you gain experience with Saltwater tanks you will surely be more careful and not make little mistakes that end up n death. Nature is the survival of the fitest and we all make mistakes.