Yes - all Stadia purchases were fully refunded - software and hardware (Chromecast and controllers).
Google also released a firmware update for the controllers allowing them to be used as generic Bluetooth controllers. It was the best Google product sunset I have experienced.
Google sure gets a ton of flack (and deservedly so) for unceremoniously axing beloved products that don't quite bring Google-scale revenue, but this sunset sounds beyond incredibly respectful to their users and really shines a positive light on them. The controller thing is such an unnecessary but trust-promoting thing to do!
Google also released a firmware update for the controllers allowing them to be used as generic Bluetooth controllers. It was the best Google product sunset I have experienced.