Considering the fact that they didn’t even have the sealift capacity to project their armies across 30 miles of channel, the question is a pure [and purely unintersting] hypothetical.
There was an excellent movie made in the 60s called “It Happened Here” about a fictional German occupation of Britain.
A more interesting question would be what would have happened if they had a better leader and later actually had something militarily effective as a payload on the V2.
Basically, they would have won the war, except for the gross and continual strategic and tactical mistakes of their political leadership. IMO, the Allies were very lucky.
The only hypothetical that works in this case is that Germany delays the invasion of France by a year, scuttles the idea of heading eastward into USSR and then stabilizes the northern Africa region for the oil. Maybe out of this scenario...they take the UK by 1944, with Japan never committing Pearl Harbor and the US stays out of the war entirely. Maybe by 1948, an invasion might occur with a stronger and more industrialized Germany. Although most economic guys will tell you....by 1942...they were insolvent and simply consuming other people’s cash.
The better what-if is if Pearl Harbor had never been put into the plans (the original idea would have avoided getting America into the war at all).
Just so...As I recall, my third grade buddies and I discussed this very issue while walking home from school just before summer vacation. We got down to the nuts and bolts question, "How fast could Superman throw all the German U-Boats into outer space?" The author would have stood no chance in debating us, none at all. ;>)