I figured you'd say that. However, it's more complex than that to actually prove it. Specially when the assets you are referring to seem to be DAZ assets that can be licensed to anyone. Recreation or reverse-engineering and parody all has special conditions under the law.
Proving it is a matter for lawyers and courts. Whether or not it's legal or ethical doesn't depend on proving the case. If Person B steals Person A's work, that's both illegal and unethical, whether or not the matter is ever prosecuted, or even discovered.
The story and the actual images (not a reproduction) in this case has more right to protection than any "asset" she's shown. Highly unethical, legally grey and mostly likely do-able without any legal recourse if the person made a few tweaks to things like names and UI.
Once again, addressing the question of provability doesn't change the actual legality. And more importantly, at least for some people, it doesn't make it right (the question of ethics).
Something like Summertime Saga where the assets are wholly created by the team would be easier to defend if this ever went to any US court. Not to mention, the issues with this if the offender isn't in a country covered by the Berne Convention.
The Berne Convention isn't the only international convention covering copyrights. There are also the Universal Copyright Convention, the Buenos Ares Convention, the WIPO Copyright treaty, the TRIPS treaty, and a few others I can't remember. As I recall, there are currently only about half a dozen nations where they don't recognize international copyrights. I know that Iran and Iraq are both on that list, as well as a couple of African countries (Somalia comes to mind, but I'm not sure.). And while China is a member of multiple copyright treaties, they have a reputation for not respecting copyright law.
So, unless you're in one of the half-dozen or so countries which don't honor international copyrights, trying to continue this (or any) game without the creator's consent is illegal, whether anything is ever done about it or not. And even in those nations, it's still unethical.