How to kill player if they aren't standing on a part?

You basically want to kill a player if their item is touching a part, right? this is a script to kill the player if either that player or their item is on a part;

-- in this example, MyKillBrick is the part you want to do the killing
function onTouched(part)
    local hum = part.Parent.Humanoid
    if hum == nil then
        local tool =  part:FindFirstAncestorWhichIsA("Tool")        
        if tool ~= nil then
    hum = tool.Parent.Humanoid 
        end
    end
    print("Good So Far")
    wait()
    if hum then
        hum.Health = 0
    end
end
MyKillBrick.Touched:Connect(onTouched)

If this doesnt work or isnt what you intended, comment on this and I'll see what I can do. If it is good, you can accept my answer ;)

IGNORE EVERYTHING BEFORE HERE

EDIT: Try this. Put these 1st script in the part you want and put a BoolValue named "TouchingFloor" in StarterCharacterScripts 1st Script:

function onLeft(part)
    local hum = part.Parent.Humanoid
    if hum == true then
        part.Parent.TouchingFloor.Value = false
    end
end
function onTouched(part)
    local hum = part.Parent.Humanoid
    if hum == true then
        part.Parent.TouchingFloor.Value = true
    end
end 
script.Parent.TouchEnded:Connect(onLeft)
script.Parent.Touched:Connect(onTouched)    

Here is the second script. Put this also in StarterCharacterScripts:

while true do
    wait(0.5)
    if script.Parent.TouchingFloor.Value == false then
        repeat
            x= x + 1
            wait(0.1)
        until x == 5 or  script.Parent.TouchingFloor.Value == true
        if script.Parent.TouchingFloor.Value == false then
            script.Parent.Humanoid.Health = 0
        end
    end
end

This will Punish the player for having none of them touch the floor (or whatever part) for over a 1/2 second. I did this because their animation might have them leave the floor for a split second. Respond if this doesnt work and i'll get back to you ASAP