I agree, a fish shouldn't get sucked into a filter unless it's sick. I have a betta in a (large) tank with a 350GPH filter and she swims by the intake with no problem.
My 6ft heavily planted tank is impossible to keep track of fish in. If one of my cories died, I would probably never know, unless it died in a visible place and I saw the body before it was eaten. Monitoring my water parameters would probably be my first hint that a fish was lost, and even then, it may be eaten before it caused problems.