The Nimbus and Supervisor daemons are designed to be fail-fast (process self-destructs whenever any unexpected situation is encountered) and stateless (all state is kept in Zookeeper or on disk).
The Nimbus and Supervisor daemons must be run under supervision using a tool like daemon tools or monit. So if the Nimbus or Supervisor daemons die, they restart like nothing happened.
Most notably, no worker processes are affected by the death of Nimbus or the Supervisors. This is in contrast to Hadoop, where if the JobTracker dies, all the running jobs are lost.
