A detail that I don’t recall seeing mentioned before
Obviously, there are spoilers ahead.
After Nikki becomes possessed, she does not tell lies from what i can remember. She may not immediately provide full or direct answers at times when asked, but I don’t recall her ever outright lying.
Also, given that Ian was sleeping with Nikki and thought she was only dating Bear to make him jealous, it’s highly possible that Ian lied to Bear about finding out Nikki’s dad’s health to drive a wedge between Bear and Nikki. I find it hard to believe that a music store employee was able to have a connection who can definitively rule out a cancer diagnosis in someone.
If you ask me, Nikki’s dad did have cancer. Which may have been a factor in her quitting her music store job. Whether it was to care for him, live her own life to the fullest, etc.