React to a Value when Projectile Impacts?

well first for the projectile we can make it so that when it touches something it will either add a Value named killer inside Humanoid to the killer's name or it will update an existing one. Also instead of creating a new script for each projectile, lets just make the event fire inside the script you are creating the projectile

--script inside "gun"
local projectile = Instance.new("blah")
--change properties here
projectile.Touched:connect(funtion(hit)
    if hit.Parent:FindFirstChild("Humanoid")~=nil then
        if hit.Parent.Humanoid:FindFirstChild("Killer")~=nil then
            hit.Parent.Humanoid.Killer.Value=plr.Name
        else
            local k = Instance.new("ObjectValue")
            k.Value=plr
            k.Parent=hit.Parent.Humanoid
        end
        projectile:Destroy()
    end
end)

Now we can use the died event of humanoid to react to its killer

--script inside character
script.Parent:WaitForChild("Humanoid").Died:connect(function()
    if script.Parent.Humanoid:FindFirstChild("Killer")~=nil then
        local plr = script.Parent.Humanoid.Killer.Value
        --do stuff with player
        --ex: plr:LoadCharacter()
    end
end)

I almost have it figured out. For some reason, the first time it kills a user, I get an error. After that, it works. How could I get rid of the error? Error:

13:26:42 -- Players.Moxeh.Backpack.RocketLauncher.ServerRocketManager:140: attempt to index local 'WorkspaceHitUser' (a nil value)
13:26:42 -- Stack Begin
13:26:42 -- Script 'Players.Moxeh.Backpack.RocketLauncher.ServerRocketManager', Line 140
13:26:42 -- Stack End
13:27:00 -- Moxeh KILLED: warlegion

The code:

local function OnHitPlayers(player, hitPlayers)
    for hitPlayerId, _ in pairs(hitPlayers) do
        DamagePlayer(hitPlayerId, player, Configurations.SplashDamage.Value)

        --MOXEH
        local LocalPlayer = game.Players.LocalPlayer
        local HitId = script.HitUserId
        local HitName = script.HitName
        local WorkspaceHitUser = game.Workspace:FindFirstChild(HitName.Value)

        HitId.Value = hitPlayerId
        wait()

        if WorkspaceHitUser.Humanoid.Health <= 0 then
            print (player.Name, 'KILLED:', HitName.Value)

            end

        --MOXEH
    end
end