This is all so strange. On the one hand, it feels very planned (Anette saying she's studying to be a nurse on the side -- what a coincidence! -- and then Floor just HAPPENS to be able to fly many miles to go on tour and has practiced the songs and knows the lyrics off by heart...yeah, sure).
On the other hand, though, it feels very...unplanned. What I mean is that I think that they had planned on Anette leaving sometime in the near future, perhaps at the end of the tour? (Definitely makes a lot more sense than this.) But something prompted them (and her) to immediately stop. Something major, because honestly, it just doesn't fit. When does a band ever call it quits with their lead vocalist, in the middle of their world tour for their very popular latest album, unless something truly serious has happened?
This also leads me to think that Anette is facing a very, very uncertain future regarding her health and that it would be unwise, bordering on stupid, for her to continue touring. So yes, perhaps she had long planned to leave, and it seems obvious that the guys had long planned on her leaving eventually, but I strongly suspect this liver cyst is culprit for it being RIGHT NOW. I wouldn't be surprised if doctors had advised her against it until they actually know what's wrong with her. Tests take time, and if it turns out that it really is something very serious (and it very well could be, liver problems are USUALLY serious), why would you want to get that news on tour, in a high-stress situation, where you are physically exhausted and you don't have your family there? She needs her family and her friends with her at this time. She needs security, and that means being at home, in a familiar place, with low stress and low strain on her body.
Hopefully it's just pointless drama, of course, but I honestly do not think that NW would be willing to part with yet another singer over some silly drama all over again. This puts them in a seriously bad position.