How could i remove a player from a Table when he died or disconnected?

You should avoid using _G as any scripts are able to read / make changes to this. Instead I would use a module script to manage this task.

There are a lot of ways this can be done but for this example I will show a self contained process which will return a round object. The idea behind this is so you would then be able to expand the functionality of what a round is.

-- module script code
local f = {}
local plrServ = game:GetService("Players")

-- vars
local curRound = nil

-- returns the cur round object or nil
function f:GetCurRound()
	return curRound
end

-- roundTime, the time for this round
function f:NewRound(roundTime)
	-- example validation for rounds
	if curRound then error("round is active cannot make a new round") end

	local round = {} -- our new round object
	local conObj = {} -- active event connections
	local endTime = tick() + roundTime -- cal total time of round
	local totalPlayers = 0 -- player count for round
	local plrList = {}
	
	-- to avoid duplication of code
	local function rmPlayerFromList(plr)
		if plrList[plr] then -- if plauer is in the list
			plrList[plr] = nil -- remove player
			totalPlayers = totalPlayers - 1 -- dec player count
		end
	end
	
	for _, plr in pairs(plrServ:GetPlayers()) do
		if plr.Character then -- check for a players model ?
			local hum = plr.Character:FindFirstChild("Humanoid")

			-- check humanoid is not dead
			if hum and hum:GetState() ~= Enum.HumanoidStateType.Dead then

				-- add this valid player to the list
				conObj[#conObj+1] = hum.Died:Connect(function()
					rmPlayerFromList(plr)
					print(plr.Name, " died")
				end)
				
				totalPlayers = totalPlayers + 1 -- inc player count
				plrList[plr] = true -- the value is just a place holdder
			end
		end
	end

	-- add the player removing 
	conObj[#conObj+1] = plrServ.PlayerRemoving:Connect(function(plr)
		rmPlayerFromList(plr)
		print(plr.Name, " left")
	end)

	-- returns the player count for the round
	function round:GetPlayerCount()
		return totalPlayers 
	end

	-- returns true if the round is still active
	function round:IsActive()
		return tick() < endTime 
	end

	-- ends the round and curRound variable
	function round:End()
		for _, con in pairs(conObj) do
			con:Disconnect()
		end
		
		-- cleanup
		conObj = nil
		totalPlayers = 0
		plrList = nil
		curRound = nil
	end
	
	-- returns an array of players in theround
	function round:GetPlayers()
		local lst = {}
		for _, plr in pairs(plrList) do
			lst[#lst+1] = plr
		end
		return
	end
	
	-- set this as the active round
	curRound = round
	return round -- return round object
end

return f -- return our table of functions 

Example script

local round = require(script.Parent.ModuleScript)

while true do
	local newRound = round:NewRound(10)

	while newRound:IsActive() do
		print(newRound:GetPlayerCount(), "Players in round")
		wait(1)
	end

	print("round end")
	newRound:End()
end

I know this is a lot to work with at first but the round object returned is safe to use in other scripts. Please comment if there are parts of this code you do not understand and I will add additional info below.

Usefull links

OOP in Lua

OOP in Lua dev forum

RBXScriptConnection

Hope this helps.