I don't think its a question of whether the USSR could have won on the eastern front without lend lease, it is whether nazi Germany could have won, which I don't think was possible, they were far too overstretched, just like Napoloeon. Germany did not have the resources to blitzkrieg all the way to the urals and wage a maritime war against Britain, Russia would have just waited until it's industry was completed beyond the urals and then would have been able come westward, lend lease only made it easier imo.
As for a possible British commonwealth/free French invasion of Vichy France, if Indian manpower could have been more effectively mobilised the commonwealth could have easily fielded more troops than the USSR! The main problem would have been equipping them. This is only if Imperial Japan stayed out of ww2.
Germany would have had to concentrate all their resources and effort either East or west to have any hope of winning on that front only, by dividing their effort they lost. Britain would have won the battle of the Atlantic on its own eventually, simply because of its greater investment in sea power. The USSR would have won eventually in the east simply because of the immense landscape and environmental conditions.
Imperial Japanese entry into ww2 widened the conflict and made US involvement in ww2 inevitable and essential.
Veni, vidi, verrimus!
I came, I saw, I swept the floor!