You can use google's search feature to search for the phrase "SEO is dead" back in time and you'll find it stated as far back as 1997 :10:
That said, SEO, just like anything else goes through the so-called "growth curve" - After a trend passes the point of steep rise, there's nothing you can do to succeed in it. In 2007 I made like 5 grand a month from writing stupid 250-word ezine articles promoting grow taller cb e-book, that has passed even the point of plateau of the curve, it's fallen fast, meaning you won't make a $1 no matter how many articles you write.
Google+, which is not very successful, even though Google did everything right with it, had a budget of billions and had access to eyeballs as good as it gets. it was created after the steep rise of the social network growth curve, which made it doomed to failure.
You can't start a new social network right now. Yet, are social networks dead? No, they are more alive than ever. There just isn't any growth potential, because of the growth curve.
Smarty-pants people saying SEO will always be alive because it means search engine optimization and there will always be search engines to optimize for, technically correct, but you know that's not what OP is asking.
People asking if seo is dead usually want to know if making a 5-page website and ordering a fiver seo service will make them rich. Guess what, if it was 2005 yes it could, so yeah it's dead.