It's a great idea in theory, but the reality is that LLMs just aren't actually very good at that kind of thing.

Depending on the temperature of the model their writing is either painfully bland and repetitive, or it's the kind of "creative" that's driven by randomness, so you'll get completely out of pocket replies that just don't fit the situation at all.

The answer to what this person is looking for is simple; find a good group to play tabletop RPGs with. Software is never going to give you that experience.