AH Challenge: Timbuktu remains wealthy and powerful up to present day

[EMT]

The challenge? Timbuktu, a city that was once one of the most prosperous and advanced of civilization eventually fell when the Portuguese discovered the Cape of Good Hope and several other trading routes to bypass Timbuktu during the spice trade and the slave trade. The challenge is to have Timbuktu remain wealthy and prosperous up to present day. The reason I'm asking this: I'm curious and really don't think it's possible, unless they start ambushing the Portuguese off the coast of Africa. Anyone feel like taking the challenge?

[sunsurf]

This would have to involve one of the local powers, I think. Mali, perhaps, remains strong, discovers Brazil, and somehow the rulers of Timbuktu take control of the Mali empire somehow...and it goes on from there. The Scramble For Africa would only involve southern Africa, or else doesn't happen at all, maybe because African disease(s) spread through Europe and discourages colonization...
The idea of Mali colonizing Brazil has been discussed in othe threads. How Timbuktu takes over Mali (or one of the other strong African kingdoms), I feel like letting others figure out.