icontrol for removing VLAN's from VS once the VS goes down

It is possible. You could pass snmp traps to a system to listen for pool down message, then use icontrol to move the virtual server into a dummy inaccessible vlan until the pool is back up. Have you tried an iRule that discards requests in the event the pool is down?

when CLIENT_ACCEPTED {
  if { [active_members my_pool] < 1 } {
    discard
  }
}