Agile was always an answer to a problem (waterfall development) that didn't really exist to any great extent. You won't even find the term "waterfall" in anything preceding the start of Agile (watch the capitalization). The classic paper that supposedly defines waterfall, Royce's paper on developing large systems, in fact does nothing of the sort and is entirely consistent with agile development. Successful teams were already agile before it was (over-)formalized. Everything you need to do successful agile (if not Agile) is pretty much laid out in Parnas and Clements' classic "A Rational Design Process: How and Why to Fake It" and Tom Gilb's Evo approach.

So, to paraphrase Frank Zappa, Agile isn't dead but it does smell funny. (And, in retrospect, it always did, we just didn't notice it in all the excitement.)