In the same way that if a compute instance fails, if a physical network node fails our monitoring systems will detect the failure and trigger the evacuate process that will ensure all affected virtual router instances are restarted on a healthy server. This process usually takes between 5 to 20 minutes.
We are working on a new feature that launches two virtual routers on separate network nodes responding on the same IP address. Once this is complete the failover between routers will take milliseconds which will most likely not be noticed. Meanwhile customers requiring Higher availability are advised to combine compute instances from multiple regions where possible.
By default your networks and instance cannot access or connect to one another across different regions. Regions are completely independent and isolated from each other, providing fault tolerance and geographic diversity. This ensures that if an instance or network were compromised by some disaster natural or otherwise; the instances in separate regions would not be affected. There are ways to go around this if you need to connect instances or networks across a region for some purpose. This can be done using Virtual private networks