The invasion may have started, but what would this have done to the Eastern Front? Less troops to fight Russia and more time for the Russians to prepare? It may have turned into a Russia vs Germany fight rather than Germany vs Allies. Plus I believe if Sea Lion had succeeded, the US would have been the next target.
If the R.A.F. hadn't beaten the Luftwaffe in 1940, could Operation Sea Lion possibly have succeeded?
Iyt would have been a hard battle. The brits were in a stranglehold and the u s would have been there with a navy presence only with u boars ubiquitous