I have also had this problem with the power couple scenario on PC no mods. Once I had one travel to a community lot and it ended the scenario saying a sim was missing. Thankfully I was able to quit and pick back up from my last save and continue playing by avoiding having the sims travel without each other to community lots. However, the last time I saved my game one of the sims was at work and when I loaded up the game it immediately gave me the message that the scenario had ended and a required person was missing. Since this happened immediately upon loading the save I wasn't able to just go back which was very disappointing having spent some time on this scenario!
