The Portuguese and Germans would not be able to justify an annexation of the Congo on such a basis. It would be an embarrassment because those countries were committing human rights abuses in their own colonies. It would be doubly embarrassing for Germany because it would violate the Berlin Treaty of 1884/5 which they presided over. Germany would have lost much of its credibility.
The only way Belgium would lose the Congo would be via a German victory in WW1. If any of the Great Powers attempted a unilateral annexation of the Congo from Belgium it would most likely trigger a war in Europe.
Oh, and I thought you were talking about a possible more recent partition - between Mobutu and Kabila, or between the Tutsi invaders and the central government. Just looked at Wikipedia and found that people call the war "the African World War".