Yesterday I came home to discover that one of the pump hoses had become detached, the result being that the pond emptied itself of water. Unfortunately, the pump settled into the lowest part of the pond, so the poor fish had no chance at all.
There will be no burial at sea - the fish had gotten pretty big - so they will be unceremoniously thrown out in the garbage tomorrow morning.
I've refilled the pond and will give it a week or so to adjust before buying some new pond fish. This episode has reinforced my decision to avoid the expensive koi and fancy goldfish and stick with the ten-for-a-dollar feeder fish from the pet store.