The scene is as follows:
Near the center of the camp is the massive crater of snow with crushed and burnt giant bodies within it. Surrounding that are the 18 tents, including Bereth's.
None of the living giants were killed. The 4 charmed ones are still here, milling about. The remaining 16 fled. Most did so immediately at Bereth's death as you were destroying the undead and the Canoloths. The ones that fled went mostly north (3 went south). They are about a minute away when you kill the last undead and loth.
The loths were summoned in some manner, as they vanish when they are killed in a fashion similar to a summoned creature. They were under the snow in wait.
The only magic detected within the circle of destruction are two among Bereth's remains; the staff and a ring. Nothing else on him remains identifiable. If he did have other items, they were disjunctioned and the obliterated. The ring is a strong Abjuration.
Your detection reveals no other active spells in the area.