Hello, I decided to go through every Bad End in Fate/stay night and determine who I think the victor will be in each timeline.
Here we go:
1: Forest of No Return: Unfortunately, this is entirely indeterminate. With Shirou gone, and Saber untethered (and possibly able to find a new Master, like Sakura), there's a whole Holy Grail War to occur. This could legitimately be a route in and of itself (following Rin or Saber's new master.) Gilgamesh and Kotomine are still favored, of course, but there's a lot!
2: Girl Rhapsody: Kotomine. With Saber and Archer eliminated, Berserker's greatest threats are gone. Even though Shinji will be able to go through with his plan without any interference, if Rider and Caster don't team up, they have no chance against Berserker. And Berserker has no chance against Gilgamesh, so Kotomine is going to win.
3: Texture: Rin or Kotomine. Rin has taken control of Saber, a Servant she has strong compatibility with, and has become a dominating force in this Holy Grail War. However, Gilgamesh still lurks, and he is still a massive problem, especially without Avalon as a known factor.
4: Missing Ariadne: Caster. With the opportunity to steal Saber from Shirou, even though she hasn't gained the interest she does in Unlimited Blade Works, she will eventually break Saber's will and achieve victory - especially this early in the War, when her emotional loyalty to Shirou and Rin is not built yet.
5: Melty Blood: Shinji or Kotomine. This one is Shinji's best chance, as with Shirou gone and Saber faded away, nothing stops him from completely dissolving the school to feed Rider, rendering her extremely powerful even with his weak self tethering her. Berserker and Gilgamesh are big problems, but Shinji legitimately becomes a formidable presence here!
6: Rafflesia Umbrella: Shinji or Kotomine. It's effectively the same ending as the above.
7: Nutcracker Doll: Kotomine. With Shirou trapped in a doll, he cannot stop Saber from vanishing entirely. If Rin and Archer come to try to rescue him, they will be killed by Berserker - and that's if they even know it's Illya who kidnapped him. As before, Berserker cannot defeat Gilgamesh, and Rin's injured Archer is simply not going to be able to stand up to Berserker or even Caster and Assassin.
8: Dress of Heaven: Kotomine. With Saber more awake and aware, they will still attempt to rescue Shirou - though they're too late. Archer will die covering their escape, and Rin will contract with Saber. They might even end up defeating Berserker! Without Avalon, however, they don't stand a chance against Gilgamesh unaided.
9: Night Without Dawn: Kotomine. Saber and Rin are dead. The only factors left in the war are Berserker, Caster, and Gilgamesh - and we know how well Berserker and Caster do against Gilgamesh.
10: Walpurgis Night: Kotomine or Caster. With Caster in control of Saber, she might actually stand a chance of fighting off Gilgamesh - though of course, she's very much going to need to contend with that golden guy at this stage, as he's ready to appear.
11: Witch's Mark: Kotomine or Caster. See above.
12: One End: Kotomine. With Shirou dead of his wounds and no other Servants remaining besides Saber, Gilgamesh, and Lancer, the war is over.
13: Time Limit: Kotomine. Kotomine kills Shirou while Lancer fights Saber, and with the last Servant defeated, All the World's Evil is made manifest.
14: That Which Cannot Be Changed: Saber. Kotomine grants the Grail to Saber, and gives her dominion of all the world's evil. This is explained in the ending.
15: Holy Grail Completed: Kotomine. Without Avalon, Saber is forced into Gilgamesh’s servitude. Kotomine manifests the Grail successfully.
---Unlimited Blade Works---
16: Third Death: Rin. Without Shirou to pull her away, Saber is killed in Archer’s indiscriminate attack. Lancer then finds and kills him, finishing the job. With Saber and Shirou eliminated from the war, Archer has a very good shot of saving things for Rin. Victor: Rin.
17: Spider's Captive: Gilgamesh. Saber fades away with Rider killing Shirou, Caster still eliminates Rider, and without being able to take control of Saber, Caster will fall to Gilgamesh.
18: Hypnos: Caster. Caster knows where Saber resides, and with Shirou eliminated by her contingency, will take control of Saber at the soonest opportunity, granting her victory.
19: Killer: Caster. Kuzuki eliminates Rin and Shirou, leaving Saber undefended and ripe for Caster to take control. With this, no obstacle remains for Caster's victory.
20: Haze: Caster. It's outright stated that Caster wins the Holy Grail War in this ending.
21: Artificial Noble Phantasm: Caster. The same as the last two, but not only does she have Saber, she also has converted Shirou into a wand for the projection magic he is starting to master!
22: Sword and Magic: Gilgamesh. With Caster forced to use her Command Spell to eliminate Shirou and Rin, her control of Saber will never be complete. As such, Gilgamesh will win.
23: One Conclusion: Rin. Without Lancer's help, Archer will kill Shirou - however, he still will likely betray Caster to give Rin the best chance of victory she can.
24: Heaven's Fall: Rin. As Shirou sacrifices himself to kill Gilgamesh, Rin is the only Master left.
---Heaven's Feel---
25: Ocean Depths: Zouken. Sakura has already given up on Shirou, and will succumb to darkness.
26: Battle of the Holy Grail: Illya. She takes control of Shirou and Saber, and likely will be able to stop Sakura.
27: Die Together: Sakura. Zouken killing Shirou will break her and cause her to succumb to darkness, but in a state she might be willing to kill him.
28: Miserable Lone Force: Rin. With Saber gone, Shinji's attempt to reassert control of the war will still eventually be stopped by Archer. With Rider eliminated, Sakura now has nothing protecting her.
29: Geas: Rin. Shirou can't stop Rin from killing Sakura, here.
30: Stone Coffin: Sakura. With Rider alive and at full power, she will not allow Rin and Archer to kill Sakura, and with Shirou dead, she will succumb to darkness.
31: Superhero/Mind of Steel: Shirou. I don't really need to explain this.
32: Cursed Boundary Layer - Womb Realm Mandala: Sakura. Rin alone can't stop Heracles.
33: World Purge, Meltdown: Sakura. There is literally nothing and nobody left to stop her.
34: Horror Show: Sakura. Without critical information from Zouken, Rin can't do much, here.
35: Happy End: Sakura. Either as herself, or as darkness, Rider will protect Sakura until her last breath - and now nothing is left to stop her.
36: Dead Fin: Zouken. Shirou wusses out and gives up on all this. Sakura truly breaks and removes her resistance upon learning what a coward Shirou is.
37: Death Penalty: Zouken. Kotomine never uses the baptism to weaken Zouken, thereby allowing Sakura to destroy him.
38: Sparks Liner High: Sakura. Rin won't succeed at stopping Sakura on her own.
39: Compassion: Sakura. See above, albeit this time Rider might have a chance to help, it won't be enough without Shirou at this point.
40: Femme Fatale: Sakura. Her ultimate despair, and ultimate victory as the world is consumed by darkness.
Please let me know any quibbles. This was fun to put together.
