They're not dead, they're just not innovating anymore. The last major update to the RTS formula was Dawn of War 2, back in 2008. Sins is an actionized version of older 4X titles, Mobas have spun off in their own directions, and Starcraft 2 is continuing the process of not doing anything new, and balancing things so tightly that you have no chance of ever seeing new strategies.
Dawn of War 2 threw base building out the window, focusing on squad tactics and unit preservation. Also, the inherent imbalances in the gameplay makes things much more interesting. With a game like Starcraft 2, where everything is honed to a fine edge, and everything is so balanced, you see singular strategies that become ubiquitous, since they are built around the maximum efficiency idea. With crazy imbalances like in Dawn of War 2, things are far more unpredictable, with some truly bizarre strategies finding success in odd occasions.
The Tyranid Gun blob is one of the strangest builds I've seen, but when I witnessed it take down a Force Commander in less than a second of shooting, I knew it was dangerous.
Strategy games need to keep pushing the boundaries of what they are capable of, and keeping things off balance to throw in that extra level of fun.