Once NC Private Email subscription expires, it gets into Grace period and remains there for 30 days. At this stage, it is not possible to access mailboxes and send/receive emails. Still, you will be able to reactivate the subscription at a regular renewal price; no data will be lost.
Subscriptions in Active
states can be renewed normally per guidelines here
If a subscription is not renewed during Grace period, it gets to the Redemption
Once in Redemption, it is only possible to reinstate the subscription at a regular renewal rate
by contacting support
Only mailboxes and emails will be restored; contacts, tasks, files cannot be restored
from this state.
If not reinstated during the Redemption period (30 days), the NC Private Email subscription gets Canceled - it is removed from the server and all the data is lost.
You can check what subscriptions need renewal in your Namecheap account - Expiring Soon section.