Hello David,
Don't worry, LFS will run as long as you can remember your password
You may delete your LFS directory entirely, than you can go LFS main page and download the LFS again and unlock. That's it, "welcome to LFS S2" .
LFS S2 user authentication is done by the special server, so your "unlocks" are stored there too as far as I know. You don't need to keep those unlocks at safe place, in fact "unlocks" are just a process of authentication of your license by internet. If you run out of unlocks (just in case), as people mention above posts, you will have two unlocks at every friday. Until today, I used three or four unlocks total for various reasons. But I have still two. Like everyone else at S2.
By buying S2, you actually make yourself a favor if you like the top simracing experience.
If you have still questions, don't hesitate to ask.