I too have faced the Dark Sorcerer, assuming you mean the enemy in the quest "The Lost Protector".  Unfortunately for me, I underestimated the strength of that encounter - the map icon said it was a medium strength army, and so I thought that my level 6-ish sovereign and my similar-level hero would be able to face it.  My hero died in the first round, taking around 80 damage from the Despair spell.  My sovereign survived that by passing the resistance check (I think she had around 25 or 30 resistance at that point in time) and fell when the army reached her.

I think the challenge of this encounter is a bit under-rated - this encounter was rated as a medium encounter when I checked it and was far more difficult than fighting several strong-rated armies of scrap golems in the Scrapyard wildlands was in 0.952 with paired level 9 heroes on horses.  I don't think that any hero or sovereign at less than level 10 or so with Hardy and Path of the Defender really has a chance at surviving the opening round unless they can pass the resistance check on Despair, because I think it's only around level 10 that champions with Hardy and Path of the Defender reach 100 health, which would leave them a low but sufficient amount to use while fighting the army that the sorcerer had with him - though they would probably still die to the next cast of Despair unless they resisted.