... who would it be and why?
My choices
Teron Gorefiend:
The first death knight to be raised once more... why not?
would also explain in a (few) quest(s) why he joined Illidan in Outland
and when he dies in Black Temple he says. "The wheel spins again...". would make sense imo.
Broxigar Saurfang:
with a bit of a stretch during the events of the legions invasion they found a portal to the place where brox died. (or sth similar how to obtain his body)
he gets buried where we raised nazgrim. so we can resurrect him.
I bet he wouldn't say no to get another chance to fight the legion
Renault Mograine:
To repay for his betrayel ofc. also like whitemane death cleansed his mind.
Leotheras the Blind:
like renault/whitemane trough death he lost his madness and is now an undead demon hunter to destroy the burning legion.
(*Darion:
acting as a fifth horsemen but didn't have to die, he just got "promotede")
who would you like to have as your horsemen?