Our ending brings us good news and bad news. We'll start with the good news first, as there's plenty of it to go around (woot). First and foremost, of course, everyone is saved. And by "everyone," we mean the people stuck on the floating chunk of Sokovia, as well as the people back down on Earth who were about to be wiped out by the would-be meteorite.
At first, it looks like a kind of Sophie's choice. Iron Man flies around and scans Air Sokovia to see what he can find out, but his best plan is to blow the whole thing up, sacrificing the Sokovians to save the rest of Earth. Captain America's not having it, though, and luckily he doesn't have to. Nick Fury shows up just in time to ferry every last man, woman, child, and dog (check out four-legged stowaway on the very last airboat) to safety.
That's all well and good for the Sokovians, but what about the rest of us schmoes back down here? Tony Stark sciences things up and, with the help of Thor, manages to reverse the vibranium thrusters inward, so that the whole kit and caboodle goes kablooey. Don't worry—it falls in (relatively) harmless chunks of rock and dirt into the waters below. The Earth is safe once again.
As for the guy that started this mess? After floating Sokovia is destroyed, Ultron manages one final cyber-getaway by uploading himself into a severely damaged, raggedy looking Iron Legion bot. The Vision is there to stop him, though. After some heady debate about the future of humanity (Vision's optimistic, Ultron not so much), Vision zaps Ultron into…well, somewhere else. He may be destroyed, or he may be teleported. Wherever he is, he's no longer a problem for our heroes.
That's not to say that the Avengers don't have problems, though. Ready for the bad news? The Avengers are disassembled. Once Ultron's handled, Hulk flies off in the Quinjet, mired in a hopeless funk. Hawkeye and Iron Man go home to their main squeezes. Thor, meanwhile, takes off back to Asgard for some Infinity Stone-related detective work. This leaves just Captain America and Black Widow to pick up the pieces.
But don't get too down. The film leaves us with more good news in the form of the next generation of Avengers: Falcon, War Machine, and the Scarlet Witch. Cap and Black Widow are all set to whip them into Avengers shape, which must mean that new Avengers movies are in our future. And that may be the best news of all.