Posting this so that it may help others.
A client performed Windows updates on an AWS server running Windows 2012 R2 today and afterwards found that the FileMaker server would not start with the error: FileMaker Server Helper quitting! Network initialization error. (CORBA::INITIALIZE)
It turned out to be the SSL certificate that was preventing it from starting. Removing the file serverCustom.pem from here: C:\Program Files\FileMaker\FileMaker Server\CStore allowed the service to start and access to the Admin Console was then possible.
After that I also removed serverKey.pem and serverRequest.pem. Then created a new SSL certificate request from within the Admin Console, re-keyed the SSL, reinstalled the re-keyed SSL and all seems well once again.
I can not explain why it happened but hopefully this helps anyone in a similar situation get back up and running quickly.