Users are asked to save the profile when exiting the Rumba program. The setting "Do not save profile on exit" in the Rumba options would only work if one user logs on to one PC but if you have several users on one PC it will ask the question again per user, each user who logs in has to change the setting within the software to not ask to save upon exiting.

Is a registry fix or a config file that can be edited so that it does not prompt to save, for all users who log into the PC?

After a Rumba install, there is a config file located in \\system called: RumbaPage.exe.config and in this file the default setting is AskToSave:
AskToSave
  

After the first activation of Rumba by the user, this file is copied to his local data file folder: %localappdata%\\ Micro Focus\\Rumba and saved under the name:
Rumba.config

There you can change the value to DoNotSave, and you are all good:
DoNotSave