can there be availability zone to availability zone communication failure but not availability zone to internet communication?
if AZ1 cannot reach AZ2 but both of them are up, maybe due to some issue on AZ1, would AZ1 be able to communicate to internet?
Edit:
I am trying to solve split brain scenario between AZs without using 3rd AZ.
Theoretically, it can happen. Each AZ is an isolated location with its own infrastructure, and therefore has separate and redundant connections to the internet. It's possible for the network link(s) between AZs to fail which would affect inter-AZ communication, but the resources in each AZ would still have internet connectivity provided you have the NAT gateways, NACLs etc configured properly in your VPC.