Has anyone played through Len’s mission in Heroes of Might and Magic II?

I haven't had three level 40 heroes at once yet. All heroes are different. But the main problem isn't even about repelling the initial attack. I could manage that by staying in the castle. The main problem is the Necromancer's advanced magic. They immediately have the Cold Wind spell at the beginning of the game. By the time I reach their stronghold, I barely have an army left. In this regard, Dwarves are good; magic doesn't always affect them.