Dunno, I'd say Unity has enough traction behind it to not suddenly disappear. It's a major contender now.
Developers write their own code in unity (C# or JS) as well as bringing in their own assets (music, art, etc). So even if the unity engine disappears, authors will be able to release their work in a meaningful fashion.
Developers write their own code in unity (C# or JS) as well as bringing in their own assets (music, art, etc). So even if the unity engine disappears, authors will be able to release their work in a meaningful fashion.