I doubt if a successful seaborn invasion would have been possible in such a short time-span (if ever) as Hitler would have needed to gain control of both the air and the sea before the invasion could be launched
(Operations Eagle and Sealion). But that is just my opinion, the Battle of Britain was won because Hitler gave up the attempt, though he came close to gaining control of the skies. Defeating the Home Fleet would have been far harder and even if successful would have taken much longer. Then the actual invasion and conquest would have used up another year at least.
But even if the UK had been defeated it would have taken too long. Ta'Samsca'Rial's point about the growing power of the Soviet Army is the critical factor that would have still resulted in a major face-off in 1943 at the earliest, by which time the odds in favour of the Red Army would be at least as favourable as they were in the Soviet 1943 offensive that started with the encirclement of the 6th Army in Staligrad. A major difference being that the start-line of the Soviet offensive would have been the Vistula, not the Volga - over 1,500 miles further west.
But you are quite right that either way world history would have been very different.