Registration date for the Cliff House name with the US Patent Trade Office was September 7, 1993 http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4809:8w346.2.14
Expiration is on the ten/twenty etc year anniversaries of the registration. So the Park Service or a new lease holder could potentially reclaim the name in September of 2023 and just use a temporary name in the interim as they did with the Ahwahnee. However, the Hountalases could open a new restaurant elsewhere with the Cliff House name and keep the trademark active. So we wil have to wait and see if the name becomes available again.