what happens if LB_FAILED is not handled

I wouldn't expect this to be a browser function. If this happens on an initial connection then perhaps you'd see an error but if this occurs midway through a session I'd expect the host TCP/IP stack to automatically reconnect if there's still data to send.

 

 

Again, you might find OneConnect useful to help with the server issue and using LB::reselect in the iRule should minimise the issue.