How to find the last player still in the game?

Hey, I noticed your code was bit messy. Here's something new that you can reference off of.

I tried to solve your issue, looks like you're doing it right, but one thing is for sure, you should be using Players:GetPlayers instead of Players:GetChildren

local DataStore2 = require(1936396537)
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local stat = ReplicatedStorage:WaitForChild("Stats")
local gamecountdown = 20

for index,value in pairs(game:GetService("Players"):GetPlayers()) do
    pcall(function()
        value.Character["HumanoidRootPart"].CFrame = spawns[1].CFrame * CFrame.new(0,2.7,0)
        --[[
        I have added "* CFrame.new(0,2.7,0)" so that I can possibly help you
        prevent players from glitching in the ground.
        ]]
        table.remove(spawns,1)
        local gametag = Instance.new("BoolValue")
        gametag.Name = "gametag"
        gametag.Parent = value.Character
    end)
end

repeat
    wait(1)
    stat.Value = string.format("Time Left: %s",gamecountdown)
    for index,value in pairs(game:GetService("Players"):GetPlayers()) do
        pcall(function()
            if #game:GetService("Players"):GetPlayers() == 1 then
                local datagold = DataStore2("Golds",value)
                stat.Value = string.format("Winner: %s",value.DisplayName)
                datagold:Increment(5)
            elseif #game:GetService("Players"):GetPlayers() <= 0 then
                stat.Value = "Everyone died..."
            end
        end)
    end
    gamecountdown = gamecountdown - 1
until gamecountdown <= 0

stat.Value = "Game ended..."

for index,value in pairs(game:GetService("Players"):GetPlayers()) do
    pcall(function()
        value.Character["HumanoidRootPart"].CFrame = (workspace:FindFirstChild("SpawnLocation") or {["CFrame"] = CFrame.new(0,0,0)}).CFrame
        --[[
        Here's another suggestion:
        "(workspace:FindFirstChild("SpawnLocation") or {["CFrame"] = CFrame.new(0,0,0)})" is here so that you can set a manual teleportation if the spawn location isn't found, just set CFrame.new(0,0,0) to any coordinate.
        ]]
        for _,inst in pairs(value.Character:GetChildren()) do
            if string.lower(inst.Name) == "gametag" then
                pcall(inst.Destroy,inst)
            end
        end
    end)
end

There are few things that you have to add and edit in your code, which will be helpful in finding the player with tags.

-- First, in the starting, create an empty table 
-- Line 7
local TableWithTags = {}

-- Now, we will add the name of the player in the local table created
-- Line 10 
table.insert{TableWithTags, plar.Name}

-- Now, instead of looping with the player having tag, we will loop in the table created above
-- Adjust the lines of the looping of the tables accordingly
for a, b in ipairs(TableWithTags) do
    if a[2] == nil then -- Checks if no more than one player is left 
        -- YOUR CODE
    end

    if a[1] == nil then -- Checks if no one is left
        -- YOUR CODE
    end
end

-- If you want to remove the tag from the player when he/she dies
-- You have loop through the table
for i, v in ipairs(TableWithTags) do
    if TableWithTags[i] == plr.Name then -- Checks if the name of the player killed is in the table
        table.remove(TableWithTags, i) -- Removes the player from the table
    end
end

Lemme know if it helps!