The plants you will lose for sure. I find plants in lakes to put in my tanks, very cheap As for dying fish, unless you actually see the crayfish catch the fish, there is a good chance the fish either died on its own, and then was eaten by the crayfish, or was sick on the bottom and became easy prey. Few people have actually seen them get caught, I know it happens, but I think crayfish get a worse reputation as fish eaters than they should.