Let's do it this way: After killing Arantir, Saref teleports somewhere to create an army of demons, and we'll leave the old storylines as they are, but without him. After the Unicorn Empire is destroyed and the alliance of three races (humans, elves, dwarves) is formed, he will appear in Grimheim near the Shio gates, and there will be a super battle, after which all existing Factions will be seriously weakened and won't have time to deal with the surviving demons. Saref and his followers will take over the Dungeons under the ruins of Talongard and establish their capital there.

Before the super battle, the balance of power will be as follows:
1) The alliance of Letos and the Ice King (Chimera mages, Dark Gnomes, Ice Nagas of Shannara, neutral mercenaries from the free cities, and the Black Guard, who switched to Stonehelm's side after Arantir's death)
2) The remnants of the old world (elves, humans, dwarves in a single castle, elementalists, possibly nagas)
3) The Voidlings
4) Proud loners
- Stronghold (with the arrival of the Gnolls, the fragmented Clans will unite under a strong leader and be able to compete in strength with any race)
- Orcs (the Ice King's army will unite into an alliance only after the orcs are destroyed (a common enemy will bring anyone together), after which the orcs will hide in the Dragon's Tooth Mountains, and the Desert Orcs of Sahaar, on the contrary, will create a powerful state)

As a result, the demons will cease to be a serious threat for about 200 years and will give way to our races.
It turned out well:D