Im not exactly that sorry for most tbh, there have been many other languages and engines that aren't unity, they have been doing shit for years now, people could have switched already. This now is just tip of the iceberg basically.
Im only sorry about small studios and indie devs that worked on something for years and now that.
If you can do it with databases you can do it with most other code. Shure it won't be problem free but way better than bankruptcy. And users will understand that it might be buggy for some time if you explain it to them.
And yes you have to retrain your staff but its their job.
And of course there will be library issues but there will be someone making new libraries.
Well, if the manual doesn't help me i ask a college, if he can't help we call our retired college, this guy was there when it was written and when THAT doesn't work we kinda just play around until it works.
I doubt that, devs can switch Code, Shure some game devs need to remake already written code but i think there will be someone making a code translator right now.
Well Unity Made a announcement to make Devs pay per Download and many devs straight up said their games will be deleted the day these changes are made.
Thats why i drive a Oldtimer.