As stated, slavery was part of it but not the cause of it.
You state: If the colonies had not revolted in 1776, slavery would have ended by act of Parliament in 1833, when it did for all of the British Empire.
Speculation at best. Irrelevant regardless.
You have no idea if that would have happened or not nor do you have any idea or anyone else for that matter if the South had won.
History is what it is and can’t be changed, unless you’re a liberal and want to wipe it out which still changes nothing.
“Hypotheticals” s and “What if’s” only work for deciding a path for future events.
Still, fun to speculate...
...and hypotheticals allow us to imagine the consequences of each of our planned current actions and better decide a wise a path for future events.
The inability to foresee even the most obvious of consequences of any government action is THE defining characteristic of ‘modern’ liberalism.