If I recall my L.A. By Night correctly the Sabbat rationale for attacking the Free States was they thought they'd be an easy target thanks to their disunity and such. Which they were but got lucky that at the last minute the Anarch gangs started fighting together. With the Sabbat established in Vegas (and persumably with a stronger base in the entire area in general) coming back to the West Coast might look more attractive. So yeah some Bishops or Archbishop flush on success and resources from Vegas (they're probably milking a good deal of money out of the area) might very well decide its time...