I find bar rates to be more flexible than incall and certainly less than outcall.  Rationale?  Bar take out is far more predictable for her - zero chance of a no show, she can check you out in terms of looks, mutant potential, etc.

As for whether she returns, its really a matter of the girl.  Some girls just don't like to do mulitples per nite.  They wanna make their 2 bills and get some sleep or meet up w/other friends.  Others are more interested in churn.  Some will even insist on going to their place if its nearby or a hotel in the neighborhood to expedite their re-entry.  I've been to NowBar in NY and seen a few of the girls do 2 or 3 trips out and in within a few hours.  Interestingly, one of these girls (asian jasmine) is actually known for being 100% GFE.  Last time I was there, I wanted a session with her but another guy caught her twice before I did.  Needless to say, I couldn't hack being round 3 (but another guy could!).

BTW: I find multiple hour/extended time rates to be very very negotiable in the bars.  Particularly if you're a cool guy and have a decent place/hotel, many girls will do time and a half and not return.  I guess they figure they'd rather get 1.5 times the base rate than have to troll back to the bar, get another guy, risk getting ripped off, get fucked again etc.  Sometimes, if a girl opens with a high price, I'll just say that's fine but I don't want the standard hour and done session.