The thing about the Marvel: Avengers Alliance game was that the sequel did not do as well as Disney thought it would. With the Avengers getting so much attention right now and the success of the first game, the sequel should have done better but it did not.
Disney followed up by killing off both games. According to Disney, they decided to kill off both games just so they can spend their time and effort on something better.
Of course, they not say what they plan to work on but some fans believe that Disney would no give up on the Avengers just like that and speculated that they might be working on a new Avengers game.
That is just one of the many speculation that the fans are hoping would come true. Disney has been making some odd decision when it comes to their games and the fans are not happy with some of the decision they made like the cancellation of Disney Infiniti.