Stadia is unique though that there are people buying digital games locked to the platform.
So its entirely possible when the inevitably kill it those games could just be lost.
So I hope for the people's sake that buy into it that Google won't shut it down (or at least have a way to add your purchases to steam or something), but its a different risk this time.
I think Stadia being shut down is a near certainty (and the GP comments' 3-4 years is very optimistic for how long it might survive), but I think that Stadia owners losing their games is fairly unlikely. When other digital services with purchases have shut down, there's often some attempt to offer a migration for user licenses. (I've watched Ultraviolet and Flixster's shutdowns and the like of late.) The game studios partnering with Google would be extremely upset for their customers to be dropped, and I'd especially expect games like Destiny 2 to cleanly migrate a user's data and progress to playing on another platform.
Even when Google shut down their Assassin's Creed demo of Stadia's technology, which was free, they gave everyone a game key to redeem on Steam at the end, so my guess is that's what would happen in a Stadia shutdown.
The most likely "loss" is from the hardware purchases, though Google has hedged here a bit on the fact that a Chromecast Ultra will still be useful post-Stadia. Even the controller might not go to waste if it works as a generic PC game controller.
There have been exclusives for other platforms that have eventually made their way to the PC ecosystem. I just saw Halo Reach advertised for the PC. I played the heck out of it when it came out, so I don't have a desire to buy it again, but it is nice to see it.
Their competition includes Nvidia, that is testing a streaming service that allows you to buy games through other platforms (Steam, Uplay, maybe others) and stream them from the cloud.
Hopefully they give you keys which can be redeemed in another platform like Steam. It’s unfortunate that so many people will have to migrate off of Stadia, but it’s inevitable.
If Google shuts it down, they will likely refund all games purchased. (But probably not any subscription fee)
They have done that previously with all discontinued products. Even hardware they tend to refund in full if it fails during the warranty and they don't have stock of that model anymore, or if they shut down the servers.
In my experience, it's difficult to get Google to hold up that warranty. When my Nexus 6P started to bootloop, Google refused to repair the product at all nor refund me the money (I purchased directly from Google and I did have copies of all receipts including pictures of the original package it was delivered in).
The bots don't care if they decide the warranty doesn't apply.
If Google decides to just not refund the game price or offer ownership in other ways, what are you going to do? You didn't buy a game, you bought a license to stream the game from Google's servers. You don't own anything and Google owes you squat.
So I hope for the people's sake that buy into it that Google won't shut it down (or at least have a way to add your purchases to steam or something), but its a different risk this time.