if the intention is to disable the reset button, maybe they aren’t supposed to be allowed to die? so the button would never get disabled? 
regardless heres proof, having it placed in starterplayerscripts that it doesn’t consistently work:
startergui = game:GetService("StarterGui")
disabled = false
attempts = 1
while not disabled do
local s, rr = pcall(function()
startergui:SetCore("ResetButtonCallback", false)
end)
if not s then
warn("Callback not registered, retrying... " .. attempts)
attempts = attempts + 1
task.wait()
else
disabled = true
warn("Callback Sucessful. Attempts: " .. attempts)
end
end