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."
But this isn't the only issue with the end.
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.
You could strip out the entire Hekaton arc and story, slap on some new adventure hooks, and have it as a completely separate adventure.
The Storm King's absence is likely discovered when talking to the diviner, where the following exchange can occur:
Why did Annam break the ordning? "To rouse his children from their complacency."
What must be done to stop the giants? "Find a magic conch of the storm giant king, Hekaton. Use it to visit Hekaton's court. Root out the evil therein." If the characters already have a conch of teleportation in their possession, the oracle says, "Use the conch to visit Hekaton's court. Root out the evil therein."
This part is particularly egregious, as restoring King Hekaton doesn't stop the giants. In fact, the adventure even says you can still go around facing the other giant clans. So rooting out the evil does nothing to stop the immediate problem.
Now, there's no relation between "complacency" and "restoring the status quo". Really, there's no reason to expect restoring things to reset the MacGuffin.
But most importantly, players aren't going to ask "what must be done to stop the giants?", they're going to ask "how do we restore the ordning?" And there isn't no answer for this in the adventure.
As I said earlier, you could rip out the 30 pages of Hekaton and his court at the end of SKT, the couple pages at the beginning, and then drop in a completely different ending adventure. And it would run just fine, only requiring a couple line changes in the preceding 200 pages of adventure (specifically in the temple with the oracle, directing players to the new adventure).
Which is problematic. Everything in an adventure should build and work towards the climax.