Here are some scenarios:
The best case. Humanity gallivants around the galaxy leaving landfills in our wake, with habitable worlds in a rim around a giant low-energy wasteland that's too expensive to travel through, like a phage plaque. Eventually we end up in segregated pockets.
The second-best case. Humanity gets as far as colonizing the solar system. The poorest people never escape Earth. The second-poorest people live in Earth orbit, throwing their trash out an airlock. Eventually, an ablative cascade is triggered, making it impossible for anyone to leave the surface.
The third-best case. China's reckless habit of dumping rockets, an attitude that seems to have resulted from the rapid spread of abundance, and therefore what you might call "true civilization," causes an ablative cascade all on its own, and we never get into space in large numbers. Obsessed with extracting what resources we can still access (but still refusing to recycle anything), mining out the planet becomes our only option. The whole world eventually looks like BaoGang, which I can't stress enough is a real place that already exists.
The fourth-best case, if you think we'll slow global warming but not avert it. The ongoing ecological collapse (particularly in insects, predators, and biodiversity reservoirs) removes all barriers to rampant herbivory, leading to severe erosion, yet more heating, weather events so extreme that parts of the planet become uninhabitable. Eventually, the spread of plant and herbivore diseases brought on by migrations and loss of biodiversity might make it unsafe to grow crops outside or hunt, potentially starving billions of people.
The fifth-best case is textbook global warming, where the planet survives our recklessness but we have to spend a great deal of our precious abundance on fleeing from the consequences of our own actions, which very much include petroleum extraction. The equatorial regions become basically uninhabitable, large land animals survive only in domesticity, the real estate market in Canada continues to get more vexatious, New Zealand has more billionaires than citizens, et cetera. We could have just tightened our belts, but SuperKendall said any show of restraint is tantamount to going back to our caves, so the entire state of West Virginia collapses into a giant sinkhole following a fracking incident.
And even worse than all that is what happens if we continue treating plastics the way we currently do. As I said in my first post, there are already species of bacteria that can eat polyethylene terephthalate, the plastic in disposable water bottles, polyester fabric, and magnetic tape. Ideonella sakaiensis was discovered in 2016 at a Japanese recycling plant, and at least two species have been identified in the Pacific garbage patch. These locations are both very much destinations for the flow of material—what evolves there probably doesn't travel far—but that only means the time bomb is ticking a little slower. Here's the breakdown:
1. Humans are, at all times, covered in and filled with many thousands of species of bacteria, including members of the Bacillus genus.
2. A Bacillus strain was identified in the garbage patch—and such closely-related bacteria can most certainly share genes horizontally. Humans are, incidentally, excellent vectors for transporting bacteria around the world. All it would take is some sushi.
3. If the PETase enzyme ever evolves to attack other polymers (which it most certainly will), it's not at all far-fetched that we'll face a modern version of the Great Oxygen Catastrophe, where metabolism of polymers causes a feedback loop in bacterial growth.
4. Meanwhile, the epipelagic and mesopelagic ocean ecosystems collapse due to the convergence of acidification, reckless overfishing, algal blooms, and the other effects of temperature stress. Presumably we're doing nothing to stop any of the other effects of climate change, because that, again, would be austerity, and SuperKendall opposes any interruptions to disposable consumer culture.
5. Now you can't even go outside and enjoy the ruined environment, because bacteria will eat through the hose on your gas mask.
For what it's worth, there are more drastic solutions to the beverage-bottling dilemma, like selling consumer soda bubblers that require far less packaging to ship syrup and CO2 canisters, or even (gasp) refillable metal canteens. The imagination need not stop just because the industry for one metal is experiencing a downturn.