I definitely don't think like most people here about Cass's death making her less important for creating content...
First, the only inevitable relationship is the wife, and in this case, you choose one and the other is left out. In other words, with the only inevitable choice, we already have a similar scenario...
Second, not everyone chooses all the optional relationships, so while the vast majority certainly choose as many as possible, for some people, some characters are passable...
This brings me to the third reason, which is the sum of the first two: Cass, dead or alive, isn't that different from the other optional content when it comes to sexual scenes...
Obviously, in my view...
Because in telling the story, we actually have "three" Cass (ally, prisoner, and corpse), which is one more than the "two" of the other characters, whether lovers or not. Although some are "three" as well (family, love, and corruption).