I'm sure that would have been the case. Conversely, if Hitler had not reneged on his non-aggression pact with Russia, we'd probably all be speaking German now (rather than Urdu and half-a-dozen other foreign languages! - Oops, sorry!).
Actually no - in the early 70's the Royal Military Academy at Sandhurst ran a series of wargames with the original Operation Sealion plans and several of the surviving German senior military officers taking part.
Conclusion was that an invasion of Southern England would have been stopped in Kent after a week when the Navy arrived and closed down the channel, leaving the invasion force cut off from supplies, with more than 80% of the invaders killed or captured.
Late in the war all assasination plots against Hitler were canned as the allies realised his military incompentence was a great help. On the Russian front if the german generals had been given free reign to maneuver the war could have dragged on for another couple of years.Fortunately for us, Hitler was a madman and his generals (who were excellent warriors) were too frightened of the consequences to contradict him.