Nothing serious would have happened. - 'Mutinous' army soldiers in occupied territory were not nearly as rough as mutinying sailors and disobeying replacement recruits at home. - And by that time, Wilhelm II had already been abdicated as German emperor and king of Prussia by Imperial Chancellor Max von Baden.
Even if the travelling party had been caught (the alleged danger never materialised, it was one of the many rumours constantly confusing people), Wilhelm might have lost his medals and other fancy stuff, perhaps even his moustache, and the party would have been looted for everything of value, but no danger to life and health would have arisen.