The oil industry isn’t about to go anywhere, that’s for sure. It’s just that within the next 100 years, it will probably shrink to a tiny fraction of what it is today.
Now that plastic bags or straws have been banned in certain parts of the world, the future of plastic is beginning to look slightly more uncertain than it used to, but I wouldn’t be too worried just yet. Microplastics are also lookin pretty concerning, so maybe in the very long run we’ll start addressing that as well. All of this might reduce the demand for plastic in general, but I don’t think that’s going to have a major impact any time soon. As you pointed out, plastics are too versatile to ditch entirely.
Maybe we’ll start using more bioplastics, but petrochemical based plastics will be used in many places regardless. At the moment, plastics are used pretty much everywhere, even when it clearly isn’t the most optimal solution. I think that this situation will begin to gradually change as the production and use of alternatives become economically attractive.
For instance, a plastic wrapping around a salad doesn’t need to last thousands of years. As long as it protects the salad all the way from the farm to my kitchen, It’s good enough. This sort of optimization will probably reduce the demand for plastic, but it will probably never go down to zero. There are lots of applications such as chemical bottles where long term durability is far more important.