I don't think Minecraft will ever truly "Die", as Microsoft will always port it to new platforms and might even be planning to make a new one. But the player base will decline with the release of Hytale https://www.youtube.com/watch?v=o77MzDQT1cg. As it looks like it could take over as the big game.
For us(age 25+) it's dead already. Because it's infested with kids. What makes it alive is private servers those are based on money leeching. It's really a fun game and i'll play it in Single Player. But Multi player? Hell no!