Not our lifetime. I disagree with the original poster. Often times manufacturing fresh polymer, while cheaper, uses many times the carbon content of the polymer in process energy.

Just as an example I know about offhand, isoprene rubber takes five times the carbon content of the product to process from petrochemical feedstocks. That said, recycling isn't very good either, so better would be to just not use it unnecessarily in packaging.

I do think it is better to incinerate than to recycle wrong and contaminate the entire recycling stream though. To me, ruining all the other recycling on top of lying about it being recyclable in the first place is way way worse.

And no, you cannot generally recycle PLA... I'm not sure where that is coming from. I hate that PLA (often labeled as 7 even though that just means "other") confuses everything even worse when people try to just toss it into typical compost and thus ruin the compost too. Of course it would also ruin the recycling... it would literally be better to just throw it away to be incinerated or else use good old numbers 1 and 2.

You can recycle PLA into recycled PLA filament for 3D printers. You can buy it online; it at one time was cheaper than new.

I don't doubt it, but not in standard curbside recycling bins basically anywhere.

I'd really like to know the answer to this as well. From all the research I've done in the past 10 minutes, you'd think that plastic is simply immutable and indestructible, and that even after millenia has passed it will still be plastic (even if in smaller pieces). But the Google SEO on this is dominated by environmental groups trying to emphasize the short-term life cycle of plastics, and it's hard to find anything with a longer-term perspective.

I think if you wait long enough (billions of years) then the landfills will eventually be under miles of earth and subjected to high enough pressures that they fundamentally change; in the same way sedimentary rock can change into metamorphic.