The Mahdist revolt nearly defeated the British on several occasions, and could have been a major turning point for British Colonial power. While they also fought the Ethiopians on the side, there may have been an opurtunity for a divergence with them. Since Ethiopia wanted to ally them to drive out the British and Italians together, but the Mahdists refused them over religious zealotry. What if they had instead gone into a secret pact, maybe with some Ottoman secret backing as well, similar to how the Ethiopians and Ottomans had plans to work together in driving the Italians and British out of East Africa.
If they could have formed such an alliance secretly, while to the public still being at war, with some raids for good show, they could supply eachother and block the British from getting troops where they need them.
This would also save the Mahdists and Ethiopians all the troops they wasted by fighting eachother, which could have made the difference against the Italians and Britsh.
Could this have the potentials to let the Mahdist consolidate power in Sudan, or at least Northern Sudan? Would they be able to push further into Egypt? Would Ethio[ia be able to drive the Italians out of Eritrea if they didn't have the Mahdists to deal with?