"But if all the leavers change their minds and vote "Remain" where will this sudden flash of 'intelligence' come from?
Answer me that!"

No sudden flash of intelligence required. We've wlll had two and a half years of learning-curve brexiteer bullshit to inform us. We know a lot more now, in particular about all those issues that the June 23 2016 brexit brigade thought would be so easy. The Irish border, for example. And they won't all change their minds. Some of them will though. Which is what you're scared of.