In Google's document (actually, it is Play Console Help though), it is said that:
Deactivate or reactivate a base plan
You can deactivate a base plan to prevent new purchases. It does not affect any existing subscriptions.
But, I'm wondering what happens when the existing subscriptions automatically renew since it is not written there. I think it's absolutely natural that they are blocked from renewing since the associated base plan is deactivated, but I'm not 100% sure if it is true.
Is there any official statement about it? Or does anyone know about its actual behavior from real experience?