ResourceManager failover isn’t available in HDP 2.0, it is going to be soon in the subsequent releases.
To your specific question, depending on whether RM can preserve work across restart or not, RM fail-over may or may not retain work. Work-preserving RM restart is a work in progress. So today, when RM fails over, all apps are restarted. For apps like MapReduce which implemented recovery, jobs will continue from their last saved progress.