Well, What I understand here about "emergency exit"mean; If critical VIP goes down/unavailable. In that case traffic move to other VIP without any impact, right?
This can be achieve via either Priority Group Activation(Load Balancing Method) or iRule.
iRule--> Create two VIP on LB. Apply iRule to VIP-1 to move traffic VIP-2 if VIP-1 fails.
when HTTP_REQUEST {
if { [active_members [LB::server pool]] == 0 }
{ HTTP::redirect "http://VIP2.com"
}
}
Refer Link On Priority Group Activation
Available Member(Pool_xxx) assign to VIP
1) x.x.x.x:xx Priority 10 2) x.x.x.y:xx Priority 10 3) x.x.x.y:xx Priority 10
4) a.a.a.a:pp Priority 20 5) a.a.a.a:pp Priority 20 6) a.a.a.a:pp Priority 20
If minimum available member will be lesser then 1 then traffic will move to other pool group servers.