Symbolism is tricky in D&D at the best of times. It's not a traditional literary form and doesn't confirm or follow conventional storytelling techniques. Even when done well, that type of ending can be particularly weak, feeling like deus ex machina and having no apparent cause-and-effect. (Very literally, since it involves Annam and the Dungeon Master hand waving a solution.)
And any action the PCs could take at the end could arguably do the same; stopping any of the giant schemes has a similar symbolic resonance.
In this case it's particularly weak since the restoration of the king isn't the end of the adventure and there's no advice given to restore the ordning then. The restoring of the ordning is just kinda tacked on at the very end.
"So the children learned how to function as a society, and eventually they were rescued by, oh, let's say...Moe."
In this case the symbolism is straight-forward and traditional. The feudal King rules by Divine Right. Due to the terms of the Ornding that is made literally true for giant society. If the King displeases his gods, as Heketon does by failing to rise to face the dragons, his Divine Right weakens. Again that is made literally true in SKT via the breaking of the Ordning. The King's Divine Right is withdrawn. A traditional world-upside-down (charivari) event then takes place, in which the daughters murder the mother and shackle the father. Further symbolically apt situations arise throughout giant-dom, such as Guh's obsession (making her a parody of appropriate chiefdom) and Kayalithica's false oracle. The giants act out an appropriate turmoil in response to their King's failings. Iymrith's literal duplicity is another perfect piece of symbolism.
When the players restore Hekaton to the throne this marks forgiveness or opportunity to repent. In terms of the traditional structure, the *only* situation in which he could be returned to the throne is one in which the Ordning is restored (or restoring). We mustn't overlook too that there has been an appropriate spiritual progress: at the end the King admits that he has misjudged the small folk. He accepts a duty to make amends (by opposing dragons as his gods intend).
I think it is wrong to ignore the resolution Iymrith's death must bring, and naturally the designers - having left the PCs at level 10 - want to offer paths along which the story can continue to play out. There is nothing symbolically inappropriate in that it must take time for the restoration of the Ordning to make good. Some of the gamboling giants may take great exertions to bring back in line. Further tests may lie in wait. That is where the roleplay diverges from the Shakespearean: the play concludes, the roleplay carries on.
For me, feeling that the end is weak principally comes about from ignoring the symbolism. I find it strong.
Hekaton isn't foreshadowed. The absence of the Storm King isn't teased for the first chunk of the adventure. It has no relation to any of the problems the players are dealing with, and his capture is also unrelated to the breaking of the ordning and doesn't require that plot point. It's just introduced without any forewarning in the middle, and then still doesn't come up until the end, the last 30 pages of the adventure.
...Everything in an adventure should build and work towards the climax.
I suspect this is where our needs as DMs diverge. When I look at my own preparation for sandbox campaigns, my narratives are light touches - a motivation here, a setting there - that will unfold at the table dependent upon the actions of my players. There's little value in overdoing it because my characters might focus their attention on something I at first expected to be relatively minor. The last thing I want is everything in the adventure tightly stitched together and working towards the climax. Rather I want space to let the story unfold. For me that is why I appreciate SKT's ending: by choosing a simple, yet symbolically sound, over-arching plot, the designers provide the exact tools needed to manage a sandbox campaign. I could even overturn it - Hekaton isn't restored - everything falls on Serissa to prove herself as Queen and/or make good the revised Ordning. Reflecting on that, I think sandboxes benefit from simple, sound concepts, that are given light treatment... that will unfold at the table. The plethora of cleverly detailed short dungeons fit neatly into that.
My key criticism is that where I do invest time for sandbox DMing is on NPCs and encounter-groups. I understand why the designers want to refer to the MM, but I wish they had invested more page count in detailed NPCs at various levels (say 6-12), and encounter groups. I think the Runequest campaign Griffon Mountain is exemplary for doing that. I wish we had more of that here. I also wish the map of the north was a fold-out. For those reasons I'd put SKT at 4.5/5. It's very good. Thoughtfully worked out. Some wonderful short dungeons. Just lacking a few elements for sandbox that would have made it a solid 5.
