It's definitely not time to retire! Believe me, in Heroes 6, there are scenarios that can stump players of any level.
Are you referring to the 3rd level for Sandra? That's a good level! Is it the one where heroes from the Sanctuary constantly emerge from the ocean depths?
I haven't played through it as a Warrior yet; I played as a Mage and a Blood character. How are you getting defeated?
Are you getting completely wiped out, or are you winning but losing a large portion of your army? I always resurrected my army; there were losses, but not as significant. It's more difficult as a Warrior because he's more vulnerable to magic... Especially if the enemy hero hits him with Chain Lightning on their first turn...
It's a challenging level, no doubt! You're at a disadvantage right away because you're playing offline. You don't have Dynasty Weapons or any bonuses.