This isn't too far from OTL, since the Fulani Jihad was a major force in the region and Sekou Amada of the Massina Empire and Umar Tall of the Toucouleur Empire created huge states. It isn't too hard to imagine that an even stronger, more long-lived, and most importantly, a commander who can better prepare for what happens after their death, can reunite the historic Mali Empire.
French colonialism is a bit of an aberation, since it's easy to imagine neither the French nor any rivals (i.e. Britain) going inland and establishing direct control in West Africa, and instead bending native states to their will. Or Europeans not imposing blockades and forbidding arms trade with African states, and thus making this hypothetical Mali state too much effort to conquer (such arms blockades hurt states like Samory Touré's Wassulu Empire).
Best case scenario for the 19th century is we have a major empire created by an Umar Tall-type figure. Earlier they will use money from the slave trade to modernise, but by no means rely on it, and later they will establish industries for goods valuable to Europeans to make money. To survive, they will play off France and Britain, as Thailand did.