The client code mostly uses hostname:port to get the connection to the region server. As a side effect if a server dies and comeback, the client won't notice. This is in theory, because the regions it's looking for are likely to be somewhere else.
In any case, if we add some dead server management in the client (
HBASE-7590), we need to manage do the distinction between the server, to be sure that we're not declaring dead a server that has restarted.