> What will be prioritized when there aren't enough workers for all the current positions?

I'll give you the politically incorrect answer.

Until recently, a large population of old people oppressing a slighter smaller population of young people (by majoritarian voting patterns) meant violence.

Humans have eliminated the 3 main uncertainties that ensured some level of demand-supply elasticity : unprotected sex, starvation and violence.

So now, instead of society promptly reacting to a disgruntled workforce, we instead get slow but perpetual decline because the workforce cannot retaliate in any real manner. They can't vote out old people. They can't enforce violence. In any other world, bored-young-people would be having tons of unprotected sex and brute force replacing the old population. But, contraception allows people to engage in their most primal instinct (sex) without the resulting rise in work force.

Now, I am a 100% not suggesting that we need a return to older times. But, we need an awareness that the removal of these avenues means that history might not repeat itself and nature might not heal on its own.... because we have conquered nature.