if the land forces under Guderian had been allowed to complete the encirclement of the BEF, then it would have been a massive blow to British morale and to their army of the day. This would not have been enough in itself for victory but with one other chabge to history, I think we could see a successful invasion of Britain:-

The second requirement is for the German airforce to have continued direct attacks on British airfields and planes rather than diverting to terror bombing of London. The RAF came very close to being wiped out, and if that had occurred, the Royal Navy would have then been impotent in the channel. (But could possibly have held off for long enough through total sacrifice to stop an invasion before the winter and allow enough time to re-arm and build defences, but the diversion of ships from the Atlantic war would have led to a far grimmer outcome in the U-boat struggle)

Interesting that in both cases it was Goering's Luftwaffe that promised all and failed to deliver. Had there been an integrated general staff without factionalism, then I might be speaking German now. However, all these "what if" scenarios ignore the fundamental structure of the German Reich as a series of feudal fiefdoms warring for internal power at the same time as the Reich itself struggled for world supremacy.

The rocket issue is really a non-starter. Sure there was a lot of interesting technology out there, but the R & D effort was too late and too scattergun to be effective. A lot of crazy things were tried - we only remember the few that worked, or almost worked.

If Hitler had spent ten more years preparing for the war, he would have won it. The combination of ballistic missiles and nuclear bombs might have been developed, but even without these, a better preparation would have had better results. but Hitler had no patience, fortunately. If he hadn't declared war on Russia, he might have conquered Britain, too, but he hated Stalin with a vengeance.

Remember too, that WWII developed as a surprise to all, including the Germans who didn't realise how quickly and powerfully they would win in Europe. They literally had no plan to continue from this springboard to invade Britain. Operation SeeLowe was an off-the cuff thing and probably would never had worked, even with control of the seas and skies. They were going to tow their army across the channel on RAFTS.