It wouldn’t do to talk about the ending of Once Upon a Time in Hollywood, Quentin Tarantino’s Valentine to the film business of 1969. But you can’t not talk about endings. The movie is nothing but grand finales – a series of sunset farewells. One is for the culture that produced Tarantino’s fictional faded male lead Rick Dalton, played by Leonardo DiCaprio, another is for the blissed-out spirit of Sharon Tate, the actor murdered that year by the Manson Family, who is returned to the screen by Margot Robbie.

And another is for Tarantino himself – or at least it will be. His latest project arrived with a goodbye. This would be the ninth film of a career, he said, that would run to 10 and no more. Then would come retirement. If the promise had the air of a stunt, he has been straightfacedly insistent since. In fact, this might be it already. “If it’s really well received,” he said this month, ahead of the film’s release, “maybe I’ll stop while I’m ahead.”

Feverish reviews and a $40m (£33m) opening weekend in the US would be most people’s idea of ahead. Maybe it was fate. For a director so bound up with a most specific kind of movie culture, this could be the ideal point to call it quits, and not just because the mood of the times appears to so exasperate him. (Was it really only two months ago that he greeted a question from a journalist about the minimal dialogue given to Robbie with a deep-freeze stare and the line: “I reject your hypothesis”?)

Once Upon a Time in Hollywood is a period piece, a bittersweet giant-train-set vision of an industry town on the brink of transformation. “Hey, Dennis Hopper,” DiCaprio chides a scowling hippy, a loaded reference to the actor-director whose biker saga Easy Rider helped upend the old-school way of things under veterans like Rick Dalton.

But of course, when we gaze into the past, we have the present on our minds. You can’t watch Tarantino at work and not see his hymn to old Hollywood as also lamenting the place it has become, a behemoth humbled by time, taste and technology. If his film traces the first cut back to a mythical 1969, it comes out in a year when it doesn’t seem like hyperbole to discuss the one-day-maybe death of Hollywood.

Hang around movies long enough and you get to know an industry prone to both nostalgia – witness the 161 minutes of Once Upon a Time in Hollywood – and hypochondria. The film business has been convinced it is about to be struck down ever since it started, although some threats have been more plausible than others. (Amazing, isn’t it, to think that Hollywood survived the LaserDisc.)

Yet the end being nigh feels different now – hints of a dwindling empire are everywhere. Tarantino’s latest has an antique feel quite aside from its setting, still existing in an age where major studios spend multimillions on films with no superheroes, sold on the back of director recognition. For pretty much everyone else, that time is past. To the film-makers working up 10-minute dramas to be watched on smartphones via Quibi, the startup of the former DreamWorks CEO Jeffrey Katzenberg, the fabled Hollywood sign might as well be a Californian Stonehenge, a puzzling landmark left by an ancient order.

Streaming changes everything. Netflix is headquartered in a brown box building in Los Gatos, California, 300 miles from Sunset Boulevard. That other aggregator of eyeballs, YouTube, is based on the outskirts of Silicon Valley. The symbolism says it all – a geographical shrug at Hollywood as the only town that can put on a show, the centre of the world behind studio gates.

Now, when I say Hollywood the way I used to, it feels lazy and inaccurate. What it used to mean was power. Now, it describes a rump of companies of middling significance among the holdings of conglomerate parents, struggling to keep pace with younger rivals. (An image to ponder: Tarantino’s face when he found out Scorsese had gone to Netflix to fund his crime epic The Irishman.) In 2019, complaining about the failings of Hollywood feels like shouting abuse at a ghost.

Of course, there is one large piece of evidence to the contrary – several, if you separate out the year’s box office triumphs for Disney, proprietor of brands including Marvel and Pixar. (Tarantino’s ker-ching opening weekend only made just over half what Disney’s Lion King made in the same period.) But Disney is not Hollywood. Disney – as learned by the laid-off staff of its recent acquisition Fox – is simply Disney. The Hollywood of even 10 years ago was an eco-system, not the home of a supersized one-stop shop. The birth of Godzilla does not imply a healthy ocean.

And while Hollywood has always made blockbusters, it never did so to the exclusion of all else. But Once Upon a Time in Hollywood exists among the vanishingly small number of studio films made for bigger than pocket-change budgets without being part of a franchise. This wasn’t how it was meant to be when Tarantino crashed into the 1990s, inspiring the wave of indie desperadoes who helped goose into life a complacent Hollywood – until the financial crisis of 2008, and the studios’ retreat into safe bets only.

Only you will know how much all of this saddens you. Hollywood got a bad name for a reason, not least the gatekeeping of executives defined by greed and timidity. Now money is tighter but directors once shut out – women and film-makers of colour among them – thrive beyond what is left of the studios. It should be possible to feel a pang for the loss of Hollywood as a darkly fascinating menagerie and remember that we still have films. Tough to shed tears too for the Hollywood that allowed itself to be ruled by monsters.

Another ending is tied up with Tarantino. Once Upon a Time in Hollywood is the first film in his career made without the involvement of Harvey Weinstein, who had been a symbiotic presence since the breakthrough of Reservoir Dogs in 1992. For all the insidery buzz of Tarantino’s latest, no predatory producers stalk his Hollywood – without the violence, the film would be a PG. Still, with such weight of history between them, memories of Weinstein lurk uneasily. (In Britain, a quirk of timing last week saw the muted release of The Current War, a starry historical drama that began life as a Weinstein production.)

Yet in some corners, Hollywood had been stripped of its status long before the horrors of #MeToo. An irony of the rise of Donald Trump was that a candidate so clearly starstruck by the movies – “Trump loves Hollywood,” said his friend Howard Stern – would capitalise, half-accidentally, on a streak of wildfire populism that damned the studios as liberal-bubble brainwashers. Tom Hanks, for years dad of choice for US moviegoers, publicly counselled that should Trump win the presidency, it would be a “dark day for planet Earth”. A month later, voters went to the polls.

What could have been a graver insult to Hollywood than the election of a reality TV star as president? Yet even Trump is just one more symptom of the same malaise, to be filed alongside the movie stars overtaken by influencers in the affections of advertisers and the bleed-out of the Oscars as a TV spectacle.

For Tarantino, the time may have come when a personal trajectory collides with a wider cultural shift. He would not be the first. At the very end of the 1990s, David Lynch started work on Mulholland Drive, another movie high on the mystique of Tinseltown with another woman in peril in the Hollywood Hills and the sense of a final curtain falling on film itself.

In the 20 years since, Lynch has made just two more major projects for the screen: Inland Empire, an avant-garde sprawl shot on scuzzy digital video, and the return of Twin Peaks. Two decades on, Mulholland Drive feels like a premonition, a lavish closing-night shebang before the greater part of the movie industry divided itself between micro-budgets and television.

But Tarantino remained in old Hollywood, a diligent caretaker, tending to the legends. Who knows? Endings can be treacherous. Among observers of the Weinstein legal case, there is pained speculation about the fallout should the producer not be convicted at his rape trial this year. Could the queasiest of comebacks be ruled out? For all its nostalgia, the film business has a famously short memory. And in a world where nothing sounds as loudly as the cash register, Tarantino may find his commitment to retirement tested if Once Upon a Time in Hollywood keeps triumphing at the box office. Maybe that would be his preferred plot twist after all – the last living director left among the ghosts.

Once Upon a Time in Hollywood is released in the UK on 15 August.