Such ideas are nothing new - prominent Brexiters have been saying much the same or worse for several years now - and aren't confined to Farage's current ramshackle bevy of lowly loose-lipped footsoldiers. Here's an article from last July:
Two, 50 or 100 years: when do leavers think Brexit will pay off?
Jacob Rees-Mogg says the benefits of leaving the EU may not be felt for 50 years and hes not the only Eurosceptic asking the people of Britain to wait patiently
According to one of the most prominent Brexiters, Conservative MP Jacob Rees-Mogg, we should see the benefits of Brexit in about half a century. We wont know the full economic consequences for a very long time, he said. The overwhelming opportunity for Brexit is over the next 50 years. So, not long to go now! Amid the overwhelming predictions that our exit from the EU slated for 29 March will be disastrous, others have been marginally more optimistic. Here are some of the leading Brexit cheerleaders forecasts for when Brexit will finally pay off.
https://www.theguardian.com/politics/shortcuts/2018/jul/24/two-50-or-100-years-when-do-leavers-think-brexit-will-pay-off
And since he's regained such prominence in recent days:
Nigel Farage never promised that Brexit would be a huge success, he said on LBC radio. I never said it would be a beneficial thing to leave and everyone would be better off, said Farage who has repeatedly said we would be better off just that we would be self-governing.
The idea of Brexit "paying off" is a way of spinning the fact that all the evidence points to a sustained period - from the characteristically reality-divorced wishful thinking of David Davis's estimate of 2 years to Digby Jones's 100 years - when it won't be "paying off".
Which leaves the yearning for "sovereignty". The inevitable descent of the US's predatory free-marketers (among many others) currently waiting to pick our bones clean means that the UK will certainly enjoy the fruits of democracy - that of another country a few thousand miles away.