I donít think it will be the end of X-men. It has three TV series, three movies and another one on the way. And like a1ant mentioned, with so many characters, the franchise can go on for decades.
Only saw the two Avengers animated movies so have very little knowledge about them. But they sort of remind me of the Justice League, fighting threats to Earth and getting hero-worshiped. And their powers are wellÖ..man-made or mystical. That makes them really different from the X-men.
I donít think there will be an X-men 4
But a reboot like Hulk. And X-men being good quality-wise like Iron man or Dark Knight? If Marvel makes the movie, then itís possible.