Undying Loyalty: What a personally-focused estxíjir is (see: Blue and Orange Morality); not common – although more frequently emulated through I Gave My Word – but a recognized trait of the greatest leaders.
Also, the reason why the bandal, or dog, is the symbolic animal and avatar associated with Tárvalén, the Binder of Obligations, eikone of loyalty, vows, oath-contracts, promises and agreements and the social order.
But given the eldrae’s attitudes towards immortality, I’m guessing the “not common” cases of Undying Loyalty that do exist are literally Undying, and not merely metaphorically so.