Drenden was a powerful archmage and one of The Six, the Kirin Tor's ruling council. While nowhere as powerful as greater magic users such as Krasus, he survived one of Deathwing's magical traps. There was little mention of how seriously Drenden was hurt by the spell. He was said to be out of action for a while, but recovered rather quickly. To his credit, it would seem he escaped relatively unharmed physically.
His fate following the fall of Dalaran is unknown.
His name is likely a reference to Detective/Wizard Harry Dresden, from the Dresden Files.