Yeah that's basically why I didn't pull it out as an option in the first place, it's not always practical. A lot of your proprietary code is going to be external dependencies linked/built against, or your own IP reused from the last project. But not all of it, and I can definitely see that smaller chunk causing a lot of problems.

You need a team that does a lot of dependency management and similar things well while building it, that don't actually help them get the game out faster, to keep the problem manageable. Or a team who specialize in open sourcing games like this, which could become a thing if this was more commonplace.

it's a bit of a straw man from your side to act like the discussion is about multiplayer when we are discussing about single player campaign based RPGs or about multiplayer when the company deliberately shuts it down in favour of a new version that just milks players for more money; or about toasters that definitely don't need internet connection to function.