Kubernetes, Automatic Service fallback to another namespace
As far as I know, it is not possible to redirect traffic to a different namespace based on the existing pods or Services in the current namespace. You can select a destination for Service only by changing its YAML configuration, and it is only possible to select pods in the same namespace.
You can simplify the deployment procedure by using Helm charts. It allows you to put variables into YAML configuration of Deployments, Services, etc, and use separate value file to substitute them during installation to the cluster. Here is a link to a blog post on Using Helm to deploy to Kubernetes