Spotify's been running strong for like 13 years, GPM is about to turn 10, etc. None of those people have been bitten yet, and there's literally hundreds of millions of them.
Stadia has all the user data on the backend, _and_ is expensive to run since all the processing happens on their end too.
Now compare that to stadia which'll probably be dedicating high CPU and GPU to each logged in user, in addition to the low latency video compression hardware they're pretty much guaranteed to have?
They say they won't until YouTube music has feature parity but I don't believe it.
I may sound bitter ...
Well, sort of. But relevant to the original question posed: are users of GPM losing their suscribed content? No.
That's beside the point, though—my reply, it's parent and it's grandparent were discussing Google products generally, not Stadia specifically.
[0] I realize that Takeout doesn't support Stadia. Though, for two different Stadia titles (Destiny 2's "cross-play" and NBA2K20's "MyPlayer"), I was prompted to log into a publisher account where my data could be linked/stored or something.
Legally or ethically?