HDDs won't go away any time soon and that's also exactly what he says but the industry is nowhere close to moving as much product as it did in the past, and the number of companies has been reduced to pretty much three. Technology also isn't going to improve drastically any more while NAND storage only needs that much of a price reduction to match HDDs, currently about 15 vs. 50 Euro/TB. Not spitting distance but it's getting darn close.
It says, after all, "boom and bust" not "rise and fall".
Also, no, tapes are more cost-effective. An LTO-8 tape is about 80 Euros, that's less than seven Euros per TB (uncompressed).