By 1780 it was a matter of when and not if. The American people had been so thoroughly brutalized by the British at that point that there was certainly going to be ongoing violence as long as there were British soldiers around to shoot at. So then the British options are genocide or wash their hands of it. And the Bible says you're not supposed to commit genocide against other Christians let alone people who might be British subjects (also you need them alive to work to pay taxes and the population needs to exist as a hedge against French influence) so since that option isn't really on the table the question at that point is at what point do the British wash their hands of it.