Suppose the unemployment rate in most developed countries rose to 20%. Undeveloped countries have it even worse. Which of the big three do you see surviving? What 3rd party devs survive? What would the industry's landscape look like ten or twenty years after such an economic fall? 

I see Nintendo surviving due to their giant cash hoard, and the already successful Switch. 

MS should at least live on as a computer company. A rumored $300 Lockheart console would probably do pretty badly, but not anywhere near as badly as the $500 models. I think lifetime sales would be lucky to hit 20 million for Lockheart. Series X and PS5 would be at or below Wii U levels. Nintendo would be forced to do huge price cuts to Switch just to keep selling units above 75,000 a week worldwide. Companies might not even be able to make game consoles in a 2nd Great Depression. 

Anyway, what's your take on it? 

Sadly, I see mostly the indies taking a hit and the big publishers surviving due to lootboxes surprise mechanics, microtransactions and the like.

Sony is diverse enough to survive, Microsoft is too big and has Windows to keep itself afloat and Nintendo a ton of cash, so I doubt any of them is is any real trouble.

All of them.

MS has 130+ billion in cash reserves (let alone whatever assets they have) They could easily ride out any sort of depression. Also, I'm pretty sure if there was a depression, video games would do badly across the board, not just the 300 dollar MS console.

I think you misread my post. I was saying the $300 console would do best, but they would all suffer.