How to replace alpha or zero nodes?

What I want to do

Create procedure for DRP (disaster recovery plan) for our admins.

I want to write correct plan of actions what to do in case of one of data centers with alpha or zero will become unavailable or in case of one of alpha or zero will fail.

  1. What have to do when alpha or zero (or both) will become unavailable?
  2. And what have to if they back in few hours (or even days)?