I don't understand why they travel separately anyway. Aren't they going to the same place?
Hard to see anything short of hospitalisation, imprisonment, or death keeping Shibuya away from the club. I suppose transferring schools extremely abruptly would do it as well, naturally, but that wouldn't be any surprise. She would have told Akiba as soon as she learned of such a change.
Nevertheless, it's interesting the author chose a way of no romance but still decided to introduce such drama two chapters before the end.