
Reports are that the split was mutual. Hawn's relationship with the rest of the team had gotten "bumpy", or she was just plain being difficult. HBO isn't commenting.
Meanwhile, comment-board consensus is that Kim Cattrall would be the logical replacement, although at 55, she may be a little too youthful to pull off playing a 60-someting-year-old. Although if production on this show keeps dragging along at the pace it has, she might well be pushing 60 by the time they're ready to begin taping.