As early as 1780s the British public were already campaigning to get rid of the slave trade during the Haitian revolution debates in parliament about it raged even in 1792 there were 400k petitions against the slave trade, the act of 1807 was a result of the abolitionist side winning over, there is also that for the brits, competition and other factors led to diminishing returns of the African slave trade, simply I do not see Haiti failing, erasing all of the other factors that first led to the slave trade being banned , also the attack on the French slave trade drew an even broader base of support than the campaign to end Britain's own slave tradeYou say slavery would have probably ended within two generations. But who’s to say it would have ended? The system wasn’t going to just end on its own. There was no incentive for it to end. The plantation system was the bedrock of colonial life. Rich whites and rich mixed race earned vast fortunes owning plantations, poor whites and poor mixed race worked as straw bosses and foremen. Slavery made millions for mainland France so the government in Paris was content. Everyone in a position to do anything about slavery benefits from its continuation, so why would they do anything to stop it? Without the revolution, without the slaves taking freedom for themselves, what pressure is there to abolish slavery?
also again for the brits in the 1820s Caribbean sugar industry went into terminal decline, and thus parliament no longer felt they needed to protect the economic interests of them, so Unless the British gain Haiti which is a topic I will get in to the trade still gets abolished similar to the otl as the factors were already there before Haiti and the the brits were the ones who pushed for the congress abolition of the trade in the congress.
I except the victors to return the island the peace treaty was not harsh to France so yes the french with haiti would be more resistant to end slavery but as I mentioned in my other comment with the congress of Vienna opinion against slavery , the reason why i think the French even with Haiti would last two generations is pressure from outsideHow have the French retained Saint Domingue throughout the Napoleonic Wars in this scenario? A big reason they were able to hold on to it for so long IOTL was the tens of thousands of ex-slave soldiers coming down out of the northern plains to fight for them. Without these reinforcements I don’t see the meagre French garrison (6,000 IIRC but don’t quote me on that) holding out against the British for very long.
while I mentioned before how the brits abolished slavery because it was not profitable anymore some have challenged this and said it was very much profitable, despite the 1820s prices fell, but public opinion just really turned against it
Now If we assume that such price failures also occurred in France as they had occurred in Spain so unless like Puerto rico who shifted I think Haiti importance to the french economy declines in the 1820s with it also declines the importance of keeping slavery