Hi there Sara,
I live in western Mali, about 70 km's south of Kayes, about 500 k's west of Bamako. Firstly, as long as you have sufficient ground clearance and reasonably large tyres, and you are used to it, you can get almost anywhere with a 2WD. I met some dutch students in an old Peugeot 2WD on the Guinenan border, they had come all the way from Holland, so it is possible, but unless you are experienced I would not advise it. Plan the timing of your trip properly, between about July and October you will not get from Senegal to Bamako by road, whichever vehicle, it is just too wet and muddy. Have fun anyhow !!