You can't use that leaked code without being sued. It has to be clean room implemented or disassembled AFAIK.
Most of the EULAs explicitly prohibit disassembling - even the act itself.
The fact that it's in binary form doesn't somehow exempt it from copyright. A translation of the disassembly into C or whatever is still derived from their copyrighted material.
But using the trademark and copyrighted content from the game on a website is risk free?
Nothing is risk free. As long as the user has a legal copy of the game it is possible. Just look at OpenRCT2. You need to have a legal copy of the game in order to run it.