Short sale terms state that the remainder of balance is collectible, need to know if i have leverage to negotiate prior to settlement of short sale.

The bank can't tell you in advance exactly what the balance is going to be, because that will depend on the exact date the closing takes place, among other things, all of which have some effect on exactly how much of the sale proceeds get applied against the loan.

It's possible that an attorney could negotiate something more favorable, but I doubt it;  having a lawyer will protect you against accidental overcharges which sometimes happen when banks get sloppy (in their own favor, of course).  You're still going to come out of this with far less debt than you would after a foreclosure sale and deficiency judgment, and a lot less damage to your credit.  Don't kill this deal by pushing too hard.