Promoting Flood Risk Mitigation Act 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 (buyout practices), and (2) ways to streamline the buyout practices. The study must consider and analyze certain factors, such as current and future trends regarding repetitive loss structures that are insured under the National Flood Insurance Program and constraints on buyout practices. 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.