If a retirement was selected, would that resource appear as a negative value in the resources table, since megawatts would be removed?

 Yes, they would be shown as negative megawatts since they would be a resource being taken away from the supply stack available to meet customer's needs. 

 When we file our plan, there will be a specific column titled “retirements.” It will clearly note what number of megawatts were retired in a particular year.