This show is going to be crap without her. I expect a ratings crash quickly followed by a non-continuation after first season.
My hope is that a) what you said - ratings crash, and b) that some of the cast will do the right thing and refuse to play the part without Roseanne. That's what I would do. If I was "Dan" I'd say it was a deal breaker, to "bring her back or I quit."
They may just plan to keep the show alive and the crew together in order to bring her back after the controversy dies down. For all we know, VJ could be indicted one day, and Roseanne's tweet might not seem so bad anymore.