The Dutch Cape Colony was a strategic location for European powers that traded and conquered Asia. During the Napoleonic Wars Great Britain sought to take over strategic locations, such as the Cape Colony. Yet unlike most colonies at the time the Cape had a settler society. So if the Battle of Blaauwberg went into the favour of the settlers, the rest of the history of Southern Africa is changed drastically, but in what way?
No British return in 1806?
No 1820 settler schemes. No English preferential treatment over the Dutch. Mostly likely no Voortrekker Groot Trek in 1836. Which means no large-scale expansion into the interior. Durban could still exist (as founded in 1835) yet would not be named after the British Cape Governor of the time, probably be a Dutch name.
Indentured slaves from British India would not have been shipped in by the boatload in the 1860s to farm sugarcane in Natal. Although that would not prevent any Indians. Just not as many in such a high concentrated location. So no samoosa, breyani and vegetable curry dishes in preference. This also affects later South African/Indian connections and therefore impacts Ghandi's early professional life (if he even existed in your alt history).
The white ruled areas would have probably been restricted to the coastal provinces and slightly into the Drakensberg, as no motive to travel inland en masse. Could possibly have the development of a black tribal coalition nation develop in the Interior.
This also means, no diamonds found by a white boy in 1866 or gold in 1886. No immediate mining rush and no Anglo-Gold or De Beers mining consortium (this actually affects worldwide history, as well as the marketing campaign "diamonds are a girl's best friend"). Minerals could still be found, just the big mining rush would probably be alot later in time. Diamonds could still be found at the Orange River mouth (which probably has a different name in this alt history - actually it appears to have been named in 1779, so you're good).
No Anglo-Zulu war in 1879. Napoleon's heir had one son, Napoléon Prince Imperial. In this alt history he almost certainly would not have been with British Forces during the Anglo-Zulu War in 1879 and probably wasn't killed in an obscure skirmish ending the hope of some for a restoration of House of Bonaparte. The lack of Anglo-Boer conflict and resultant push for more land would have affected the rise of Shaka Zulu. He was probably still born but if there is no equivalent push for more land, he may not have developed into the military man he became IRL. There was probably a Dutch equivalent conflict in your alt history and if there was, I reckon it could have eventually resulted in the formation of the Zulu Kingdom being recognised North of the Tugela.
Also means no Anglo-Boer wars or at least not to the same extent. Concentration camps would have to be invented elsewhere and Lord Kitchener can go die. Churchill would have to get his first war correspondent experience elsewhere and probably wouldn't have been able to use his capture and escape from the Boers as a means of gaining public admiration as a hero and gaining political power. Also means no Afrikaaner resettlements in Chuput Province, South America after the end of the 2nd Anglo-Boer War!
There is alot that can go differently. These are just off the top of my head.
Over the last few days, I've realised that while what I wrote above is true if "the British didn't return" as asked in your title, it is different to "what realistically happens next after the Battle of Blaauwberg" asked in your text. I answered your titled question, and not what would be the most realistic response by the British.
I'm pretty sure the British would have fought back. Losing would have been a HUGE hit on their Political Pride and standing. I can't see how they would have let that stand. If you want them to not return, you are going to have to explain, in your alt history (not in your question), why they allowed themselves to be seen as having lost. What other factors played a part in this decision etc. Remember it was a completely different mentality back then. The Height of the Glorious British Empire. For King and Country. Long live the King.
Your alt history is going to have to consider what prevented them from sailing back down south with more soldiers, decimating the militant Settlers and taking the colony back for themselves. How the loss of the Cape Colony would have affected their political standing on other fronts. Where did all the people, who ended up as Cape Colony Settlers, eventually end up? India, America? How did this affect those countries. The American War of Independence was in 1812. How would boatloads of fresh English Settlers and the shame/knowledge of a previous lost colony war have affected American History. How would the Indian Mutinies in the 1857-58 have been affected by knowing that the English could be made to back down? The entire world would be different as a result of this 'one battle'.
I'm not going to list what could happen next. As you saw in my first draft, many things can be different. I'm sure you have it covered, but it takes more than one battle to explain this alt history of no British return in 1806.
Just for fun to show the wide range of affects.
More modern-day South Africans who probably wouldn't exist as we know them in this alt history (source) :
- Politics: Jan Smuts, Nelson Mandela, Steve Biko, Desmond Tutu.
- Entertainment: Hugh Masekela, Miriam Makema, Alan Paton, Toto, Charlize Theron, Arnold Vosloo, Dave Matthews, Trevor Noah, Neill Blomkamp.
- Science and Technology: Elon Musk, Mark Shuttleworth, Christian Barnard.
- Sport: Roger Federer, Ernie Else, Oscar Pistorius, Hansie Cronje.