Each subscription plan has a number of available voice slots. If you downgrade your subscription, no voices will be removed from your account, but you will only be able to access as many voices as are available on your new plan.
For example, if you created 30 cloned voices and you downgrade your tier to Starter, which allows 10 cloned voices, then you will need to upgrade to the Creator plan to regain access to the other 20 voices.
If you have a Professional Voice Clone (PVC) and downgrade to the Starter or free plans, which don't have access to Professional Voice Cloning, your PVC will not be removed from your account, but you will not be able to use it until you upgrade to Creator or above.