Promoting Flood Risk Mitigation Act (Sec. 2) This bill directs the Government Accountability Office (GAO) to conduct a study to assess: (1) the efficacy of practices or programs under which the Federal Emergency Management Agency (FEMA) provides assistance to state and local governments to acquire flood-damaged properties committed to open space use in perpetuity (buyout practices), and (2) ways to streamline the buyout practices to provide more timely assistance. The study must consider and analyze: current and future trends with respect to repetitive loss structures and severe repetitive loss structures that are insured under the National Flood Insurance Program; buyout practices, including the socioeconomic status of recipients of buyouts under buyout programs and examples of successful buyout programs, including best practices employed; administrative, financial, or temporal constraints that may impede the timely acquisition of properties under a buyout program; potential options, methods, and strategies to address such constraints; the ecological, financial, and flood risk reduction benefits that buyout practices provide; an assessment of how FEMA may use buyout programs to reduce future flood disaster recovery costs; and a cost-benefit analysis of mitigation and buy-out projects and programs. The GAO shall submit to Congress and FEMA a report on the buyout practices study and the feasibility of FEMA establishing an alternative buyout program.