Hi WichWayIsUp,
Unless you're planning to fly ZS registered aircraft, you're better off doing your IR back in Australia since you've got this far already and yes, you'll have to convert or validate your license to fly in Botswana, Zambia, Namibia, Malawi, Tanzania etc... All potential starts for a low timer BTW, don't know about right now though. Yes, you're generally hired for bush flying which is VFR flying however, many employers like to see that you have an instrument rating, not sure about Botswana in particular.
Go back, finish your instrument rating and then head out to Africa with enough money to do a little tour of the potential employment markets is my advice.