Minecraft is still receiving a large amount of new players, it's just not at the pace of what it once was, which will be the case of every single game out there.
I seriously doubt minecraft will die out any time soon, if at all. Just like jellyninja mentioned, considering it's still under development as well as having an extremely huge modding community, with mod packs coming out at an incredibly huge pace, as well as having constant videos by great youtubers, saying it will die out is a complete long-shot.