Currently the REST gateway doesn't support HA.
Meaning the client is given single port number to contact the gateway.
Clarification to region server failure part in the question: if region server process fails (but REST gateway doesn't), the REST gateway can contact other servers and continue to provide service.
@Joshua Adeleke HBase REST is just an HTTP based service so you can always add more and have a load balancer in front of it.
Or even use Knox which supports an ha configuration for HBASE.
Add the following under the HaProvider:
And the following service definition: