(I've been requested to do this since some are thinking I'm spamming the page. Obviously Avengers isn't as popular as the show Chrysalis and Sombra (on my avatar) are from, since that wiki has hundreds of comments on each article. And before you look up what show they're from, know they both die in the end. I'd do one for The Other, but it's clear he's not Ronan.)
All right, so here it is. 2012, I think, The Avengers came out, which the first five films were leading up to. Loki is working with The Other and his army of Chitauri, and in the end it's revealed they are all working for Thanos, whom Joss Whedon said will be in Avengers 3, which is 2018 at earliest, 2012 at latest. That's too long to wait for a villain defeat.
But can they defeat Thanos? I read he's the most powerful Marvel character, besides Chthon. Joss Whedon said Thanos is too powerful and they can't just punch him. Plus, I think it's been said he'll have the Infinity Stones and Infinity Gauntlet by Avengers 3. Do you expect the Avengers to train in 100 times gravity and have the power to defeat Thanos? Do you expect them to open a mystery box, get Rainbow Power, take away all Thanos's power and banish him to hell? Do you expect him to have some magic ring that if you throw it into a volcano, it destroys him? I don't think so.
Now, this film series isn't dark enough to kill all the main characters. So, I predict, and I'm 100% sure, that this will end in one of two ways.
1.) Thanos isn't the main villain of Avengers 3. One of his allies is. Probably Strucker, who I predict he'll ally with at the end of Age of Ultron after Ultron is killed. The Avengers defeat him. Then, post credits scene shows Thanos about to fight the Avengers. Either shows him stand up and tell The Other "I'll take them down myself", or shows them meet up at some arena about to fight and end it like Angel. (The film is being directed by Joss Whedon, who did Angel). It's up to us to decide what happens, but the only realistic otucome is Thanos kills them all, even the Hulk.
2.) Thanos is the main villain all the way through Avengers 3. Somehow the Avengers find some sort of weapon or power or void to throw Thanos into and seemingly kill him. All is well, Earth is saved, but post credits scene reveals he survived, and leaves it at that. The best we can assume from that is that he decides to leave Earth alone. (but would someone who wants to "court death" be afraid of fighting an enemy that could potentially kill him? Look at his reaction to what The Other said about challenging the humans being to court death.
I know it has to go one way or the other for two reasons.
a.) They can't kill off Thanos. People are so attached to villains these days but these movies are still killing the one-shot villains, like Alexander Pierce, and probably Ronan and Ultron. But the only other recurring main villain is Loki, and look where he is. On the throne of Asgard, just like he always wanted. Loki's been around for this long they couldn't kill him even with his supposed redemption and death in The Dark World. So maybe they're saving the "spare the villains for the fans" for the recurring villains like Loki and Thanos, so they can have the freedom to do what they want with one-shot villains.
b.) There's always a postcredits scene. What would the postcredits scene of Avengers 3 be about? Most of the others were leading up to the next film or a big crossover in The Avengers, or else introducing a new character. Iron Man 3 just revealed Stark was narrating to Bruce Banner. But one, Thor, reveals that the villain, Loki, survived. The post credits scene has to involve Thanos one way or another, it can't be anything else, unless an Avenger seemingly dies but turns out to survive, or else Nick Fury returns from Europe, or they decide to do another shawarma scene.