All the non-respawning Rhogar with the polesword will have a Tyrant heart near them so when you get their health to zero it will heal them so you have to destroy the Tyrant Heart in order to kill them. If you can't find it then get it's health to zero and there will be a red stuff pointing to the Tyrant heart. Destroy the unique looking pot and pick up the heart then kill the Rhogar and it won't respawn. There are 12 polesword Rhogar all of which are in the Rhogar realm but 1 will be in the Infinite Void near the Guardian boss fight.