not only would that be even more illegal that it already is, if popular enough, one will most likely get a not so friendly email from their lawyer

they bought the rights so
From who. Like how can they buy something from a company that doesn't exist anymore
They owned the copyright to the game (or it could've been the publishers). Now that has passed to Osome (or whoever owns the code+assets).
the assets would be a problem I guess; because the code is, well, from you. So we would only have to re-do the assets
No, the code itself could be problematic too (if I share the source code).
Though if you use different assets with the hsk engine, and make something new, i would assume that would count as derivative work, and not allowed (to share). However, it would be hard to prove, so I assume it wouldn't be a problem.
I'd have no idea on how the law sees that. Different countries operate different on that topic and, atleast for me, it is hard to get the sweet spot in that topic.
However there are some things I know, like patches, mods, fixes, sharing of files is *I think* allowed as long as you don't make profit out of it AND it helps the game to actually run on current system.
That is one of the grayzones. Empire Earth Reborn does that for example.
Yeah no, it is not allowed in the EU (or a gray zone), though it is not usually enforced if you don't make profit off of it.
Yes, if you have bought it legally, you may do a lot of things with it, rewriting, etc. AS LONG AS you don't share it.
Doesn't the EU have a law in the meantime that forces you to FIX or PATCH your things to work at all time

iirc they wanted to put that in action, but no clue if it is actually active
it does, for interoperability
Now what is the case if the developer just doesn't do it
You can't generally patch the game to work as you want. However, if it doesn't work, you CAN investigate/patch to make it work.
That is the case for private things, but for public? Like I can't imagine there is nothing you can do about that
What do you mean for public things?
`Yes, if you have bought it legally, you may do a lot of things with it, rewriting, etc. AS LONG AS you don't share it.`