Yes @Gougagna, you'll regain access then to your claimed free games, see here:
What happens to my claimed free games if I’m no longer a Stadia Pro subscriber?
If your subscription to Stadia Pro expires, you will lose access to your claimed free games. When you reactivate your subscription, you will regain access to your claimed free games with your save data intact.
that seems weird, normally you should be able to resubscribe at any time again for Stadia Pro, see here: Managing Stadia Pro and game subscriptions
You have two ways of subscribing to Stadia Pro again, you can try via Stadia app or via the webbrowser on stadia.google.com, see here Purchase a Stadia Pro subscription
If you have problems, try to check the following and try again to resubscribe after each step:
If nothing works, I would recommend to reach out to Stadia support as normally there shouldn't be any problem to resubscribe to Stadia Pro.
I can confirm, as it is, there is no way to get to the resubscribe flow through the settings or account info. The only, as mentioned above, is to try to launch a game like Destiny 2, and it'll ask you to "Resubscribe to play".
Alternatively, on the web, this takes you right to it: https://stadia.google.com/premium
But yeah, there's currently no button from the settings / account page, on either web or mobile.