Return Employees to Understaffed Work Sites to Reopen Now Act of 2023 or the RETURN Act of 2023 This bill requires each federal agency to submit to Congress and publish on the agency's website a plan for the agency to resume in-person operations. The plan shall, among other things, include the agency's policy with respect to permitting permanent remote work for employees who can successfully achieve their duties away from their official work sites, metrics to measure the productivity of employees performing remote work to identify employees that fail to fulfill their duties, a plan to provide essential government services in person for individuals in the United States, and measures to prepare for future public health emergencies that can be quickly implemented if remote work becomes necessary. Each agency must submit a report to the General Services Administration recommending termination of the agency's leases of physical work spaces that are underused.