I would think it will be remembered as a day of reclaiming complete sovereignty in all things Great Britain. I am happy to see America pull away from "global" entities and agreements.
My inference from history is within a few decades Great Britain will rejoin the EU (or some similar pan-national organization) when the current spasm of nativism in the world subsides.
I have yet to read of any explanation of what tangible benefits the UK will derive from this action, which will cost it approximately 50 billion Euros and a loss of a few percentage points of GDP.