Yoon Son Ha of Runaway Plan B might have to leave the drama. Less than halfway through the series, she was rear-ended on her way home and it led to a fractured leg that she may need surgery for.
If she gets that surgery, it’s more likely she will have to leave the drama, but she’s a crucial part to the mystery that there will be plot holes if she leaves. I’d say, if she disappears, I think they could use that part of the script to their advantage as they try to figure out where she went while solving the mystery in other ways. The other characters will just have to rely on others to give them the information they need – or to provide the threats and obstacles that they (sorta) need.
Her surgery is scheduled for October 31, and she will need at least a week’s recovery.