I think there are two things going on-- first is the money bit, which we've all talked about-- and that is that the band likely won't sell as many records or as many seats on tour without Stevie. This of course is what they pay managers and lawyers and agents etc to worry about, so chances are that those folks around the various members are concerned about this and giving them advice on how to deal with it, which may well include "you should wait for Stevie". On the other hand, I think the band also has concerns that if they go forward without her, she will use her platform of the media to make either openly disparaging or negative remarks or more passive-aggressive ("damning with faint praise") kinds of remarks. She has in the past used this threat to get what she wants with the band ("How will it look if I go to Rolling Stone and tell them this or that"). She has learned very very well over the years how to use the press to get her point out (funnily enough I thought of this while recently watching an old piece about Princess Diana and a lot of the perspective of the presenters was about how she was much more savvy at exploiting the press than Charles to get people on her side etc). So I wouldn't be surprised if there was concern within the band or their circle about the risk of her giving interviews about how "disappointed" she was that the band for whom she's given up so much (cutting off the Bella Donna tour etc etc) didn't find it in their hearts to wait for her or whatever. (even though she's pretty clear if they wait for her to join them on a record they'll be waiting a very long, long time). And then they're in the middle of a potentially ugly media sh&tstorm and the band goes out on a really publicly sour note. It just feels like they are feeling between a rock and a hard place. I'd bet Lindsey is all for releasing something but Mick clearly is hedging his bets Stevie will change her mind and I feel like Christine is also hedging even though she wants to get the new music out.
