Question

Some domains don't have a renew button in RCP (e.g. .at TLD). How does one renew such domains? Will they be lost after they reach their expiration dates?

Answer

Some registries don't allow for explicit domain renewal or, sometimes, the renewal call can only be made within a certain period of time before the domain's expiration date. If the domain page in RCP were to be queried on June 1 2020, for the domain that expires on June 29th, the Renew button would not have been present:

For instance, in the case of .at domains, when the 'Expiration date - 28 days' period comes, the Renew button will appear in RCP allowing to increment Expiration date Openprovider without actually sending a renew command to the registry.

In cases like this, the renewal behaviour can be controlled by setting the auto-renewal policy (be it per domain or the global setting) to On in one's RCP account. 

Going back to the .at TLD, to renew an .at domain one simply has to set the domain renewal mode or default renewal mode to Auto renew.