Most fish are more than willing to eat both veggie and meat. They are also opportunistic feeders...so if it's there, they'll eat it, even if it's one of their own kind. That being said, if something unfortunate happens and you lose a fishy or an invert, take the dead out and don't let it foul your water (you'll have an
ammonia spike that could be deadly to your other fishies). But if you are missing one and can't seem to find it anywhere in the tank, chances are it died and became a food source for others.