@jjrandorin and
@MP3Mike, thanks to both of you for considerate, non-insulting replies (unlike the earlier replies from others). I agree that it shouldn't be the service center's problem to need to deal with migration of things like the game's save data, and it should be something I could do manually as needed.
As for if I had been warned about the progress loss, no I don't think I would have turned down the upgrade, but I likely would have played the games a lot less in the time before the upgrade, not gotten so invested in my progress, knowing it was temporary. The ability to sync data between cars (including resiliency for situations like this) would be awesome, much needed feature that they'll hopefully add soon.
Especially frustrating in this particular case is that just a couple days ago, I spent a while with a friend, setting up a game of Stardew Valley with them, customizing the character, etc. They were looking forward to continuing their adventure next time I saw them, but now I'll need to tell them that the save file has been lost, and they'll need to start over if they want to continue playing. If I'd had some advanced warning I wouldn't have started a game with them till after the upgrade. Also not finding out until picking up the car totally ruined what should have been the fun excitement of the FSD feature preview.
When taking a computer in for service, the staff always will ask if you've made a recent backup, say how they can't guarantee there won't be data loss, even if they're doing something that shouldn't have any effect on your stored data. I would have expected Tesla to do the same thing, at least for something like this that is guaranteed to wipe out the data.
Also some data wasn't overwritten, as the Music Favorites we're still saved, so it's clearly possible for data to be persistent across computer upgrades.
Also to clarify
@Twiglett, it's not the scores I care about significantly, but the experiences in the game that can't even be accessed without redoing the rest of the game now. I had done everything up to the final boss in Cuphead, but now if I want to experience that boss level, I'll have to spend hours doing every other level again first. That's what I care about, not the number of points.