Nothing happens
That is what they should know it will happen. Nothing.
If you don't want to argue it, then go ahead and close this thread since your problem has already been solved by the code being open source.
Will the user be warned about the default coordinator? Until they are, thread remains unlocked.
I don't mean to repeat myself, but if nothing happens, why is a warning necessary? A warning implies there is some risk incurred if it is ignored, but there is no such risk posed to users of the software.