how much of the short sale balance with the bank come after?

I can't opine on Virginia law specifically so this is a general discussion of how these things work.

Some debtors have been able to negotiate to have the bank "forgive" the short-sale deficiency, however if the home is not your primary residence that can result in having to pay income tax on the amount "forgiven".

In other cases, the banks will not agree to it, but selling the home will at least fix the amount of the deficiency so that if the market declines further your exposure doesn't grow.

As a practical matter the key thing you want to avoid doing is executing a new note ... UNLESS that note is for a seriously reduced amount and the amount of principal forgiven that you will be taxed on is low enough that the whole thing taken in toto is a good deal.

The reason to avoid executing a new note is that the bank will sell the deficiency to a junk debt buyer if they don't sue, and the junk debt buyer may have a hard time laying its hands on that original note. And without the original note their lawsuit against you may fail.

The one thing that I would say specific to Virginia situations is that I have heard courts are relatively lenient with creditors presenting "affidavits of debt" which are the typical way creditors with weak documentation (such as lack of a note) try to get around the swiss cheese holes in their own cases. In other words, technical defenses that work for debtors in other states sometimes are not so effective for Virginian debtors.