We are leaving an awful lot of plastic in the environment.
This means that inevitably, some microbe will evolve the ability to digest one or more kinds of plastic. Over time, more microbes will evolve the ability to digest ever more kinds of plastic. If you understand how evolution works, you know that this is inevitable and that it will probably be microbes that evolve the ability to digest plastics first because of their short lifespans and high reproductive rates.
When that day comes, plastic will become something that can rot. That means plastic will lose the one of the major reasons plastic is valuable to manufacturing. When that day comes, our economy and our whole civilization is going to have to make some major changes. The more plastic we put in the environment, the faster that day will come.
The entire plastics industry might disappear simply because we didn't do enough to recycle plastic and keep it out of the environment.