The NTSB does not do what-ifs in the sense of calculating expected body count had an accident not been averted. They do, however, often investigate the performance envelope involved in an incident/accident and the timeline for possible corrective actions. So in an investigation it's quite common for the NTSB to look into how initiating corrective action at different points in time would have affected the outcome. e.g.: Sentences like "the pilots could have [taken corrective action X] until Y seconds before collision is a pretty standard sentence to see in an investigation report.

This kind of information is important for determining the available safety margin and the proper changes to recommend in order to prevent similar incidents in the future.