That sounds like that wouldn't hold up in court, it's not a "white room" implementation by any means. I hope it won't be tested though.
Contrast that to OpenTTD or OpenRA where they (AFAIK) re-implemented the engine while still having the same approach of re-using the main games assets.
Edit: taking a look at the source code, I don't think what you're saying is actually true. RollerCoaster Tycoon 2 was written entirely in Assembly but I cannot find any Assembly files in OpenRCT2. So unless they already finished porting everything, it seems incorrect.
I looked at the source a few years back and saw more than a few functions that looked like the result of decompiling machine code to C. I didn't spend much time trying to see if that's true or not, but in the end it doesn't seem to matter. Still, if you like the game, you should keep a local fork of the repository, just in case.
Contrast that to OpenTTD or OpenRA where they (AFAIK) re-implemented the engine while still having the same approach of re-using the main games assets.
Edit: taking a look at the source code, I don't think what you're saying is actually true. RollerCoaster Tycoon 2 was written entirely in Assembly but I cannot find any Assembly files in OpenRCT2. So unless they already finished porting everything, it seems incorrect.