They don`t have money to last until 2050. They have money yes, but how long it will last for depends on how much of it they spend... and even more importantly, how much of it their investors will let them spend. It could last until the year 3000, or they could blow it all in a year (that one be one great party at Nintendo HQ for a year though! )
They aren`t making money from every console sold. Firstly, I haven`t heard anything to suggest that the Switch will be selling for more than it costs to make, but even if it does that still doesn`t mean they are making money. There are a whole lot of other costs to consider other than basic material costs and shipment, the marketing budget for one, the years of R&D for another. The Switch will start with quite a significant net loss (as every console does) and until they can clear that amount they won`t really be making money from each console sold.
As for games, they don`t even get 100% revenue, let alone profit. Retailers take their cut, taxes take a cut and games do cost money to make as well. As for 30-40% of third party games (what third party games? ), I very much doubt it`s anywhere near that high. Probably more around 10-15%.
And Amiibos? Yeah, they`ll make money from them but just like the software the point isn`t that they could make money by going 3rd party, it`s that they could make more. They sold a lot of Amiibo`s when only the small number of Wii U owners could use them, now imagine how much more they could have sold if games that utilised them were playable by the billions of people that own a PC or phone or something.
As impressive as Nintendo is, third party do amount for something, namely in the handheld place. Companies like Level 5 basically survived with Nintendo the last couple of years after wasting a lot of resources on WKC.