I have added a new restart method for reestablishing the connection to the server in Net::OpenSSH version 0.80. It is something that should have been available a long time ago, but at first it was difficult to implement, then at some point I had to revamp the code managing the master process in order to fix several others bugs making it trivial but didn't though about adding it... until I read your post today!

Note that it is possible that a broken connection goes unnoticed until you actually try to use it. wait_for_master cheeks the local ssh master process but some kind of errors (for instance, a broken TCP connection), would go unnoticed. So to be sure you cover all the cases, you need to try running the command and if that fails, reconnect:

my $cmd = "...";

my $out = $ssh->capture({timeout => 120}, $cmd);
unless (defined $out) {
  warn "unable to run command $cmd, retrying...";
  $ssh->restart or die "Unable to restart SSH connection: " . $ssh->er
+ror;
  $out = $ssh->capture({timeout => 120}, $cmd);
  unless (defined $out) {
    die "definitively, I can't run the command $cmd: " . $ssh->error;
  }
}
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If $cmd does some non-atomic operation, it is a long running operation you don't want to run twice, etc., you may like to use a harmless dummy command as "echo hello" instead.