And jumping around won't help much here. If you jump ahead before completing the quest, it's a defeat. The heroes won't be able to pass through the gates. The only thing you could do is defeat the yellow hero with a strong hero like Gurnir. But since I managed without him, now the only thing I can do is gather an army from all the cities for Krilon and maybe give him a slight boost (but there aren't many buffs available).
And even then, this tactic might not be necessary.
Perhaps, if you play from the very beginning, you should focus on developing Death magic instead of, for example, Nature. In the final stages, there are strong opponents with robes and guardians, and he has so many altars for tactics that are essentially wasted. It's unlikely that you'll find the Staff of the Dead (I encountered it in one of the parts, but I don't see it in this one, and it's quite rare)