Not everyone would need to save or invest. Each individual employee would not be collecting the full value of what they produce. They would all be collectively collecting the full value of what they produce via the business. Management still exists, money still goes back into business. This isn’t some fantasy scenario, it actually exists successfully in the real world. Mondragon is the most cited example. Just because the enterprise is collectively owned by the workers doesn’t mean that each worker is in full control. It means the firm is run democratically, collectively.