Dumb question, can you reassign an already assigned public IP address to a different EC2 instance?
Let's say GP's micro instance goes down, or extra load brings the need for a larger instance, can they spin up a different EC2 instance and reassign the existing public IP address to it?
Absolutely, this is done on AWS with EIPs (elastic ip's). You can migrate an EIP between instances via the AWS API and the change takes effect nearly instantly.