You should probably have a Consul server in each availability zone if you want to protect against this type of failure.

Consul uses one raft cluster per "datacenter", so you don't have to worry about write performance seriously degrading as you scale, it will only be up to the max of the number of availability zones you'd like to operate in per region. Plus you shouldn't be doing write heavy KV operations with consul anyway.

Just because you are using strong consistency doesn't mean you can't get reasonably high availability in practice.