Decision-making & giving feedback
Assuming that humans could remain as decision-makers at any high level, e.g. defining what type of life humans want to enjoy, what they would like the world to look like, what constitutes happiness, etc, the need will exist to specify (and most importantly give feedback on) those goals, objectives and to keep refining them and adapt them to new preference frontiers.
One could argue that the above constitutes work, and can definitely have both a meaningful and significant impact in the economy.
I think we call the above "programming" or machine learning (~ automatic programming from data) in today's world.
Nowhere is written that our ultimate goal in life is fixed/static. Moreover, computing our goals and preferences over time, and as we evolve, may be an unsolvable problem and require infinite time & feedback.