i don't know anything about the Heidenau because i never saw it.
i travelled through zim, and was on tar 95pc of the time. balance was good gravel. so, dual sports will be fine. eg metzler tourance, bridgestone battlewing, michelin anakee.
botswana - if you want to do the makgadikadi (or however its spelt) you need serious sand tyres. i am not good in sand, and with a brand new karoo rear tyre and tkc on the front, i was still bad. this was on f650 twin which is also 19" F and 17" R but 50kg lighter than your R1200. if you want to do the pan i suggest michelin desert on the rear, and karoo or tkc or mt21 or whatever on the front. getting the bike up to 50-60kmh was the issue (so need rear traction) more so than handling on the front end.
other than that, all botswana is tar. you can't take bike into the dirt/sand of chobe (you can ride from zim across bots into the caprivi tho). likewise no go for moremi or kalahari on the bike. i took a 4wd which i hired out of maun, and was very very happy to not have the bike. the sand tracks are nasty.
in south africa, i didn't get on the dirt. if you do the garden route and keep going to either maputo (along the coast) or north into lesotho then tkcs or karoos will be fine. if you don't do those sections, again, dualsports are the way to go.
i didn't do zambia - from the people i met who travelled here, dirt tyres like tkc are adequate. there are some fun mud sections, sand not such an issue.
namibia. here i think go the tkc front, and dualsport rear. in gravel its nice to have grip on the front, but it is dry hard gravel so the dualsport rear will last longer than the tkc.
i think you will go through more than one rear tyre for that many km. if you are starting in cape town and doing namibia, RSA, bots before zambia (provided you're not trying the salt pans of bots), i'd start with tkc or dualsport rear (probably tkc but it won't matter coz you have to change at some stage, and the tkc will last long enough), and karoo or tkc front. then i'd buy (in nelspruit RSA near kruger, before going north to zim or east to moz, buy the desert or something new for the rear.
i'd budget 13-15,000km on the tkc front before its shot, and 6-9000 on the rear. karoo similar, desert less. on my tourances and anakees i do 30k front and 20-25 rear.
chuck a 5L spar brand water bottle on the back, or take an ortlieb 4L bladder minimum extra (over and above camelback) for salt pans (1 night) and general riding in namib.