Exalted. In second edition, the Sidereal Martial Art Obsidian Shards of Infinity Style actually has a charm that allows you to choose a bittersweet ending, forcing fate (i. e. the storyteller) to resolve the conflict in one of several different ways.
Battle for Macragge: Hive Fleet Behemoth was stopped...After it consumed hundreds of world, killed billions of people, and completely wiped out Ultramarines 1st company(1/10 of their fighting force). And it was only a scouting party.
That's just in the numeric sense. First Companies tend to hold the veterans and elites of the Chapter. An entire Company, the Tenth, is also composed of pre-Space Marine stage Scouts.
Behemoth wasn't really a scouting party, just the first of many.
Another Tyranid example would be the battle between Hive Fleet Kraken and the Eldar of Craftworld Iyanden. The Craftworld survived and Kraken was destroyed, but by the end, four-fifths of the population were dead note at least in the traditional sense: thanks to their soulstones, Death Is Cheap for the Eldar, and Prince Yriel was bound to the dreaded Spear of Twilight.
Promethean: The Created: You have spent years, perhaps centuries, as a reanimated collection of dead flesh. You've struggled to fulfill your Pilgrimage, created another of your kind, fought off the Pandorans, and fled from the hatred of humanity. Your reward? You lose all of the mighty powers you had, your durability and your strength. You are frail, weak, vulnerable. Your memories may very well evaporate. You still have to live in the World of Darkness, which is just as much of a Crapsack World as it sounds like, and now you have no defense against it. You are human. You have a soul. Your journey is complete.
Vampire: The Masquerade ends this way in the fourth Gehenna scenario, "Crucible of God". Basically, a Class 2 apocalypse has taken place: civilization has been pulverized by the war between humans and vampires and the rise of the Antediluvians that followed; the environment has also suffered considerable damage- particularly during the Lasombra Antediluvian's reign of terror. Outside the relative safety of human settlements, the wilderness is swarming with bands of murderous psychopaths created during Malkav's reign, along with giant ghoul animals bred by Absimiliard, and hideous mutantscrafted by Tzimisce. On the upside, with your help, Saulot has been able to call down the wrath of God on Tzimisce and bring an end to the Curse of Caine; the few Antediluvians that managed to survive Gehenna and ascend into godhood are benevolent enough to leave humanity alone; and though you've lost your immortality and your powers, you're no longer troubled by the Beast or hunger for blood, and you can help rebuild human society with a clean slate.
The second optional ending to the scenario involves you remaining a vampire; in part because God has decided to keep Caine suffering a little longer, you've been transformed into a second-generation vampire, and given the option of creating a new Kindred society alongside the emerging human nations. Still pretty gloomy, but at least you've got power on your side.