When Jens Bergensten joined Mojang (to work on Scrolls), Minecraft was quite advanced and already had the nether and red stone. Notch did not rely on any store and was using his personal paypal account that got blocked due to an anomalous amount of transactions.
It was “quite advanced” but at the same time very much in its infancy in terms of the timeline of the game.
I personally don’t think the game would have gone as far as it did if it continued as a solo project.