How do I keep models in workspace when they fall into the void without causing performance issues?

So, to expand on my comment and explain it better. I recommend putting the model in ReplicatedStorage. This is extremely useful, it doesn't cause lag plus its always there when you need to clone it again! There's different ways to go about respawning (aka cloning) the model after this so below I will provide you with what I personally use. Also I highly recommend checking out this link! https://developer.roblox.com/en-us/api-reference/class/ReplicatedStorage

--First off you want to put your model in ReplicatedStorage
local model = game.ReplicatedStorage.Cars.RedCar1--im assuming this is your model so this is what I'll use 
while true do 
    wait(5) -- regenerates the model after 5 seconds theres other BETTER ways to do this! you can always use a button or a ontouch function
backup = model:Clone() -- backs up the model so it can respawn
    backup.Parent = game.Workspace
    backup:MoveTo(Vector3.new(-105.042,203.5,100.995))
end
--i didnt test 

Here's a on touch script that works!

local model = game.ReplicatedStorage.Cars.RedCar1
wait(1)
function onTouched(hit)
	local check = hit.Parent:FindFirstChild("Humanoid")
	if check ~= nil then
		local player = game.Players:GetPlayerFromCharacter(hit.Parent)
			script.Parent.CanTouch = false
			script.Parent.Transparency = 1
			script.Parent.CanCollide = false
			local backup = model:Clone()
			backup.Parent = game.Workspace
			-- you can use this to set the position versus where it was originally backup.Position = Vector3.new(-105.042,203.5,100.995)
			wait(5)
			script.Parent.CanCollide = true
			script.Parent.Transparency = 0
			script.Parent.CanTouch = true
		end
	end
end
script.Parent.Touched:Connect(onTouched)

I hope this helps you. I'm happy to help. If you have any questions don't hesitate to ask.