Having been through a similar process with KPMG (that ended similarly), I can confirm that they operated on a retainer basis and it did need to be re-upped from

Having been through a similar process with KPMG (that ended similarly), I can confirm that they operated on a retainer basis and it did need to be re-upped from time to time. The vast majority of their remuneration was a success fee though. This is pretty standard for the industry.