HA Vlan FialSafe Question

if i have failsafe enabled on one external vlan at both units ( active & standby )

let's assume that this vlan post is down on both units , both units will try to failover to each other , what will happen ?

 

with my Juniper firewall i have command on HA called " master always exists " , is there similar one at F5 , this will ensure that in such case one box will be the master