IIRC, the job of putting down the Maritz Rebellion was left entirely in the hands of the South Africans, including many who had actually fought against the British in the Boer War. Since South Africa had been granted Dominion status in 1910, the British had no role to play in putting down an internal rebellion unless the Boers had asked them to.
Therefore, if you had a harsh crackdown, it would have been a Boer vs. Boer situation. The perception of many leaders as being British stoogies would have been greatly enhanced, and you would have had a great deal of trouble, with many Boers heading out to join forces with the Germans in German Southwest Africa and German East Africa. Trouble, indeed.