Are you sure there won't be legal problems? The company closed, by the owners still retain trademarks. At least I think so.
I also think that they had an official contract with those who originally invented the game world. You know that it's based on comics? So, I think you also need Vertigo authorization.
And about RenPy - you think this engine will be good enough to make a game of good quality?
For some time, I also considered making an interactive movie game, though based on another novel. I decided that I am not ready for such risk: if the company that INVENTED this genre failed, I am not ready to risk money.
And to you, I just wish you luck. If you will be allowed to make sequel, and it will finished and released, I'll be happy to try it.