"The breaking of so great a thing should make a greater crack," said Octavius Caesar on hearing the death of the Roman military commander Mark Antony; the revelation – he suggested – "should have shook lions into civil streets, and citizens to their dens". Dramatic perhaps (these words were put in Caesar's mouth by Shakespeare, after all), but what can be sadder than a final hurrah and a goodbye forever?

Centuries later, Robbie Williams' schism from Take That was no less traumatic for many, with Samaritans setting up a helpline in 1995 for fans who felt suicidal at the news of their idols' evacuation from boybandland (they had no clue at this point that he would be in possession of the sort of singular talent it takes to make an album such as Rudebox). Even when Bonehead left Oasis to spend more time with the family, we all gasped and asked what would become of the people's champions.

When it was announced that Gwil Sainsbury had departed the 2012 Mercury prizewinners Alt-J, a shrug might have been detected in Cambridgeshire, a "meh" or two around the country and some "bofs" in French-speaking territories. Some said "who?", and they were just the Alt-J fans. A proverbial tumbleweed was syndicated from newswire to newswire as readers worldwide failed to give much of a stuff about the signing off of a founding member of a band whose debut, An Awesome Wave, has done great business, selling in six figures. Sadly, such monosyllabic grunts of indifference are symptomatic of our times, since the glut of charismaless musical troupes, of which Alt J are the reluctant figureheads, makes the "faceless" DJs of the 90s look like colourful eccentrics in comparison.

If you're wondering which was Sainsbury in Alt-J, he was the smallest, fairest one, the one who looked most like a gap-year student in his brother's hand-me-down ski wear. The others can be seen slouching around in beanie hats, hoodies, surf shorts and espadrilles. Hey chaps, take your musical sense from Brian Wilson by all means, but not your dress sense, eh? When Quietus editor John Doran held up a picture of the sartorially bereft group set in the foreground of a beachy mise en scene for the legendarily fastidious Bryan Ferry to survey during a recent video interview, such was the scowl on the majestically cool one's face that it was as if Narcissus had just been offered some Groupon vouchers.

Was it amicable or was Sainsbury pushed? Does anybody really care other than his mum? One must ask, is this the least earth-shattering musical news event in history? Let us go one further. This might in fact be the least significant moment in the history of history, and its implications for the universe are as yet unknown. What will happen to the space-time continuum when Sainsbury doesn't leave the band in a parallel universe and yet the same insouciant shrugging and noncommittal expelling of the word "arsed" ensues? Will this quantum nonevent cause the multiverse to implode, sending us on a course of backwards time travel without us realising it? I'm doubtful.

When the quiet one in the band did something mutinous in the old days, it would be insignificant in a really understated way on a slow news day, but it would at least threaten to register with the people nevertheless. Think of John Deacon refusing to be inducted into the Rock and Roll Hall of Fame, think of that previous Arctic Monkeys bass-player guy who left the band because he was scared of going to America or something, think of Antony Costa from Blue going into the jungle for I'm a Celebrity all on his own, or Edele from B*Witched sticking it to Sinéad (or was it the other way round?) on The Big Reunion – these are the quiet ones making themselves heard without having to do anything as nasty as invent a bedroom tax.

In the case of Alt-J, it's a quiet one leaving three other quiet ones, a moment in pop surely unprecedented. Sainsbury is the most anonymous member of the most anonymous band in popular culture, in an age in which – we are constantly told – no one even cares about bands anymore. Why don't we all just pack up and go home?

Perhaps only Alt J themselves can save us now. When they advertise for a replacement, the ad should read: "Popular folk-step combo looking for bass player; only zany guys/girls need apply. Immaculate threads, a winning personality and a penchant for the theatrical essential. No time-wasters."