We could replace a large number of plastics right now and be just fine. Society flourished and thrived before we used plastic for everything in our lives. Some people would make less profit though, so of course it's impossible to make those kinds of changes, but we could.
Well, the mainstream adoption of plastics following World War II happens to coincide with an unprecedented period of relative global stability known as the “Long Peace.” So there’s at least some version of “thriving” that was, in fact, not previously achieved. Correlation does not imply causation but in this case it’s difficult to disentangle which innovations have lead to the relative global prosperity that has enabled this, and I think plastics are on the shortlist.
Society flourished without lots of stuff we have today. It just flourished less.
And people aren’t failing to migrate away from plastic because “somebody would make less money”, they’re using plastic because everything else basically sucks in comparison. It’s tough, cheap, light, stable, easy to shape, doesn’t often break dangerously, can have all of its basic properties modified, and more. Nothing else is THAT good.
Edit: Not to mention, it’s not as simple as “don’t use plastic packaging anymore”. We pull oil into a machine and cook it off at various stages to produce various things. Turning cooking stage 8 of 12 into a worthless pile of garbage to be discarded doesn’t stop us from pulling in that oil for the other 11 uses.