We will have plastics forever.

It will become more expensive when we have to pay for the energy embedded in it, but the difference is not significative on almost any end-product.

Oil is a finite resource, although we keep finding new deposits so the numbers on "we only have 10 years left!" tend to be hyperbolic.

With our current exposure, it is estimated that 40-50 years worth of oil remains, although there is likely to be new locations found and an overall reduction of oil usage in the coming years.

PLA plastic as commonly used in 3d printers comes from plant materials not oil. We know how to make any plastic from pure CO2 (and whatever else needed for the atoms) - however the massive amount of energy needed to do so makes it uneconomical.