I like to end campaigns, when and where possible.
SWd6 - Blew up the 2nd death star, flying the B-wings. 1 year campaign.
AD&D, the Dragons departed for another dimension, taking magic with them, which had been prophesied for about 2 years, real time.
Conspiracy X 2.0 - the Agent team, sent to rescue a surviving Templar, blew the job, got him killed by Al-Qaeda Terrorists at a dock in Cairo, after a strike team of Al-Q failed to take out the team with an RPG, car bomb, and rooftop snipers, but the team on the defensive, just barely failed the mission. They instead torched the bad guy's merchant freighter, and quit Aegis, figuring there was a mole / doublecross somewhere. 6 months campaign. Loads of fun.
Top Secret S.I. - The agent team finally found the Russian Ex Spetznaz leader of the bad guys who had been terrorizing the USA, and went in with commandoes and Titan Teams to lay waste to and shred the bad guy desert base near Death Valley, Nevada. 9 months campaign.
Traveller - After having been screwed over and chased by Naasirka for about 15 sessions of play the team headed to Vargr Space, to try and set up new lives as alien artifact / goods dealers. 6 months campaign.
Twilight:2000 - After having travelled from near Lodz, down the Vistula, All sorts of things...saving a convent of Nuns from marauders, doing all sorts of things that could very well be classified as war crimes by friendlies, took the train, and heading towards germany, what survived of the unit, (with 150% casualties already, were mostly marauders themselves) took on elements of a Russian reinforced tank platoon in a small nowhere village on the north German plain, and after a series of incredibly unlucky events where most friendlies were killed by tank fire, or crushed by tank treads, the last guy suicided himself against the last T-72 with an AT mine, to save the village. We all agreed enough was enough, and ended it there, after a year and a half of play.
I hate it when games just .. die. I've had that happen, also, many times, mostly because players stop showing up, or political problems among the players.