What if Cumberland had joined Exeter and the other cruisers at the River Plate?
Short answerGraf Spee would be sunk in this counterfactual, although the British could still suffer severe damage.
NotesCumberland would make Graf Spee's position untenable by adding a full County-class cruiser to Exeter and the two Leanders. Graf Spee's avoidance of Cumberland supports that judgment. In this counterfactual, the German ship would be sunk. The British cruisers could still suffer horrendous damage.