Which version of HBase are you running? If we have a node or two go down in our cluster, HBase is completely unaffected. Recoveries can take up to a few minutes, in the old ages it took hours.
I know that MTTR (mean time to recovery) is being worked on together by several large companies to get down to seconds.
Sorry, I should have clarified. When a node goes down, there isn't any sort of "minute" interruption...When there's a full scale outage and you need to perform an actual recovery, that can take minutes.
Also, if you use the Thrift service as an interface to HBase (we do), you can have it running on several machines on the cluster and be able to set them up using a failover architecture - as long as the cluster itself is healthy, Thrift should work from any machine you have it running on.
I know that MTTR (mean time to recovery) is being worked on together by several large companies to get down to seconds.