Unity has temporarily closed its offices in San Francisco and Austin, Texas and canceled a town hall meeting after receiving death threats. The company made the call as a precaution against possible retribution after it announced a contentious change to its business model this week.
Dude...Just stop using the software and let the business fail. That's all you've got to do. Unreal engine, Godot, Gamemaker Studio, Source 2, QBASIC, use something else.
Depending on how much money you expect to lose, that may be the more prudent option for some.
At the very least you'd have something to work with - it's not truly "from scratch".
I work in the AAA industry and I've ported code from one engine to another - it's not fast by any means, but at the very least you can assume the code that's there is largely correct. The killers are materials/shaders, porting over design work, and fixing timing issues. If you have netcode that can be tricky as well.
But at the very least you can have the core of your game running again reasonably. It's how things like Stanley Parable: Ultra Deluxe went from Source to Unity, and how Pokemon BDSP went from the proprietary Pokemon engine to Unity.
Indies and AAs can hire some extra hands to work temporarily with their existing engineers to port and they'd probably lose less money than Unity is charging.