Oh, Earth will eventually recycle all of the molecules in the plastic, at least that which is exposed to erosive forces and not sedimented down to be preserved for millenia. The question is how much disruption, poisoning, death, and destruction it will cause as it contaminates everything, is sucked up in the massive recycling systems, and filtered through the food web over and over. We're going to find out the hard way and there won't be much we can do but watch. My guess is that it is at least partially responsible for the insect apocalypse and severely disrupts the microbiota of most ecosystems. It's also probably pretty bad for human health.