No unfortunately not. The most important ones are code assets.

For instance I use heavily modified versions of:

- PuppetMaster from http://root-motion.com/ - Chronos from https://ludiq.io/chronos

Trying to fake the API surface area of these assets would be... hard. And without them the game is entirely non-functional.

I've seen other devs open source their games and simply release it in a non-functional state with statements clarifying what's not included, why, and what it would take to get things up and running. Just about anyone looking to build a modern game from this sort of source release is going to know what they are getting into with or without these assets and may still get value out of the release even if it doesn't provide all the necessary bits to create an executable.

You could still release what you can. Might be helpful as a reference or for modders of your game.

Could you theoretically supply patches to those libraries alongside your code? I'm curious what the legal implications of that are.

It's possible, but the patches would be tied to a very specific version of the asset. Unity has made this easier recently by making asset store assets part of the package manager, but my stuff predates all of that.