There's quite a few people from the GG days that absolutely hate Ralph, people he slandered on his blog. The first one that comes to mind that would absolutely sue if Ralph started talking shit is Wu, maybe even Zoe. Luckily for Ralph these people have seen what a shit life he has and where he is headed so they gave up on attacking him. But if Ralph were to lie/slander and publish it, I could absolutely see them going after him.
Obviously Vickers would since he's been looking for a legal way to fuck over Ralph. There may be more but it's all very dependent on what Ralph writes (if he ever does it, this is not the first time he's talked about writing a book).