Ok, I'll go a bit deeper.
Shawna, and later for the same reason, the Asian girl in the Massage Parlor, were placed in game for the sole reason of giving way to some early sex scenes. Giving the MC a bit of time to establish and nurture deeper relationships with other girls.
They weren't meant to stay in the game after. So, they haven't. By everyone insisting on it, MoonBox made a compromise, they will return later. In Asiko's case, maybe she already did, in a much, much later scene in Part 3. Shawna's part is yet to come. The relegation to the End of the game, isn't even a certainty, it is however, LATER. The When, How and Why is not known by us at this time.
If there are decisions made about it, they haven't been shared here.
Peace