SC2 is certainly smaller than it was in its heyday, but I don't see it going away anytime soon. I think going f2p is largely what's keeping it alive. It's still a hard game to learn, but I think it's got a fairly well thought out on-ramp with custom maps, co-op and 4v4s as relatively "safe" modes and a series of logical steps for eventually getting comfortable with 1v1.