Having a think about multiple endings for gamebooks. Traditional and open-world.
Types of Endings
Many older gamebooks such as Lone Wolf and Fighting Fantasy had three types of endings.
The unique ending where you are victorious (typically page 400 in Fighting Fantasy). You've found a path through to the true ending and can be rewarded (or go onto the next book)
Second is the "instakill" one where you are told "Your Adventure Ends Here" or something similar. Your character is dead, trapped, lost or left without any path to proceed forward. There are no numbers to turn to.
Then there are the times you can't continue because your character has died. They are out of Stamina, Endurance or Wounds and died mid-passage. Sometimes it might be in a petty or funny situation.
Some gamebooks would have multiple version of the "Victory" page. The Choose Your Own Adventure books, Heart of Ice and Nightshift. Lost in the City from December in the 100 Endings Book Club. In Scorpion Swamp from the Fighting Fantasy series, you could find the plant for the "Good" ending, make a map to a town for the "Neutral" ending and get some wizard amulets for the "Evil" ending (which itself had a couple of variations).
To me having more then one ending is a big plus. There are reasons to replay it, there are different ways to play it and reach victory.
Open-World Gamebook Endings
The first open-world gamebooks I played were Fabled Lands (by Dave Morris and Jamie Thomson), and I don't remember them having any of the victory endings. You either played until you died (without a resurrection deal) or retired your character (or got bored of them).
There was no over-arching plot so this makes sense. And there might be victory endings in later books I've yet to find.
The first open-world gamebook "victory" ending I found was in Highways and Holloways, Book 2 of Steam Highwayman. There was a place you could retire to become a doctor serving on an airship. It wasn't an ending to one of the plot themes in the series (such as a large one in Book 3). It was simply your character finding a different ending that they were happy with.
I loved the idea of ending partway through, and determined to add a few such endings to any open-world gamebook I wrote. I also liked the idea of unlocking something, such as a new character ancestry, a piece of equipment or a bonus to your stats the next time you played. Isle of Torment by Dean Moodie also does this, unlocking new captains and giving stat bonuses on subsequent playthroughs.
The second open-world series by Dave Morris and Jamie Thomson is VulcanVerse, and that does have a definite ending (or series of endings) in Book 5, after you performed the labours of the other books. I've yet to get that part, but it means the series has a very different emphasis that Fabled Lands.
One other thing I loved from Steam Highwayman was the point scoring at the end. This gives another incentive to play certain ways (or can simply be ignored). Seas of Blood from Fighting Fantasy has this (gold collected),
Finishing Up
So what's your favourite ending in a gamebook?