cmiiw,
so Death Sentence is needed to lock the Ride Summon in place.
If the player doesn’t do Death Sentence, then the summoned ride will disappear on its own after a while.
But there’s also 24 hours time limit on Death Sentence so players can’t exploit it by targeting random thing then leave it alone to have free permanent summon, and it came with extra penalty.
It forces Dullahan players who want to take advantage of their racial skill to have play style revolving on targeting an enemy daily and stalk it around.