When a member stops paying for their paid subscription, depending on what you select, they'll either be removed from the paid group automatically (remove from group option) or they'll be shown a paywall and asked to update their payment info (require resubscription option).

The remove from group will still give them access to free parts of your community, but they won't be able to access any of the paid content. The require resubscription option will make it so that they cannot access the community at all, and they will need to resubscribe before they can access the community.