When the surviving members of Led Zeppelin - singer Robert Plant, guitarist Jimmy Page and bassist/keyboard player John Paul Jones - gathered in London recently there were two items on the agenda.
The first was the launch of Celebration Day - the DVD/Blu-ray/double CD of their December 2007 reunion concert - but the second was that question which dogged the solo Beatles for a decade: would they get back together again?
Plant was largely dismissive of the idea as he has reframed his career with the Raising Sand album (with Alison Krauss), his Band of Joy and now the Sensational Space Shifters, who have just completed a South American tour. Jones said he seriously doubted it and Page reminded everyone that the Celebration Day concert was five years ago. So, "if it was going to happen it would have happened by now".
Even drummer Jason Bonham, who sat in for his late father John, accepted this had probably been a one-off.
And think about it. All are in their mid-60s, with Page perilously close to 70. So the short answer is "no" with that "never say never" coda added.
Which means Celebration Day might just be the full-stop on a remarkable career that broke records for ticket and album sales, stamped dozens of songs into the collective consciousness of generations and still sees their name on teenagers' T-shirts.
As a concert film, Celebration Day is extraordinary. Director Dick Carruthers gets the cameras right into the sweat zone and the rapid editing - like a Bourne movie - keeps the excitement edgy and palpable. If the sound seems a little underwhelming in the first couple of songs - the opener Good Times Bad Times, which starts with "in the days of my youth" and the lesser Ramble On - everything settles and Led Zeppelin reveal again they were a force of nature, like rolling thunder cut across with flashing lightning, a ground-shaking noisequake during which buildings fall as electricity whip-cracks across the sky.
Celebration Day - the deluxe edition DVD/Blu-ray with an extra disc of rehearsals - is big stuff and Bonham the Younger such a formidable powerhouse - especially in the thrilling enormity of the kerthumping Kashmir, and Whole Lotta Love, where Page plays theremin - that his father is hardly missed.
And, like a garage band, they huddle close on the large stage as a tight focal point in which Jones watches Page and Plant with such concentration you'd think he was auditioning and terrified of making a mistake. His nervous intensity adds tension behind Plant's still-cocky swagger and Page's mercurial magic, which pulls from old blues and a nuclear explosion with equal assurance. When he stands inside a pyramid of lasers and pulls out a violin bow to attack his guitar, it is pure theatre.
There's also an infectiously good spirit with laughter, a few fluffed lines and missed cues - but then again, too few to mention - and Plant conceding some songs you just have to do. And they do.
Most of their signature songs are in the 90-minute set, but those two openers (and For Your Life, the coke song on their 1976 album, Presence) were never played in their entirety when they strode across the planet four decades ago like behemoth rock gods, which might explain the hesitancy.
Does this translate to CD however? Surprisingly yes, although if Led Zeppelin meant nothing to you, if you despise them for the excesses they came to stand for in the pantheon of rock, or if you just thought their music sometimes sounded like an explosion in a guitar factory (it does, but that's actually a good thing) then Celebration Day in any format won't give you reason to change your opinion, or celebrate.
But if you believe rock is about taking risks, then this - for men of their age, the weight of expectation and the possibility of it going haywire after all those years away - was risky business.
It was also loud, freewheeling, shamelessly excessive and cleverly calculated.
The question is not, therefore, "will they do this again?" but "could they?"
Celebration Day - whatever you make of it - teasingly offers both answers.
* Celebration Day in a number of CD/DVD and Blu-ray formats is available now. A three-record set will be released on December 7.