atonal is a very strict term, and I don't think I know a lot of pieces strictly atonal. Gardener is talking about a serialist composer, not an atonalist!
But, exactly like Gardener, if by atonal you mean dissonance, lack of major/minor, weird harmonies, not based in triads, etc, then no by all means it's not dead at all! If you actually mean the early forms of atonality then the world has probably moved on.
I could also argue that in some parts of the world (London for example), serialism never caught on and moved on, as well as musique concrete (except Birmingham). While, as Gardener points out (yes, I'll stop refering to him at some point!
) in other places you need t obook 6 months in advance! So...