Apparently the Hountalas family trademarked (not copyrighted) the Cliff House name back in 1992. A trademark must be renewed every 10 years. Part of the renewal process is a Declaration of Use, basically stating that the trademark holder is still using the trademark for its original purpose. Assuming the Cliff House name was trademarked back in 1992 (seems like that could have been challenged at the time because of its prior use and/or because of NPS ownership of the building), it should be coming up for renewal in 2022. The Hountalas family could not truthfully declare that the trademark was still being used for its original purpose, so the trademark should expire then and someone else could use the name. Of course, a new operator of the restaurant could also purchase the trademark from the Hountalas family.