Backup Virtual Server

Unless there is some other reason to create a separate virtual server, you do not need to use two different virtual servers for this.  Just use Priority Group Activation on the pool instead.  
One virtual server (VIP-1, 10.10.10.100).  One pool with priority group activation enabled and set to "Less Than... 1" with 4 pool members; 192.168.10.100:priority 10
192.168.10.200:priority 10
172.16.10.100:priority 0
172.16.10.100:priority 0