Challenging Times part 1

Friend/Client called with a question for their parents. The parents live in another state. This particular state has been one hit the hardest, always being mentioned as one of the top 4 states with highest depreciation of real estate values. While Austin/Metro Austin has been experiencing troubles since November 2008, this market has been "feeling it" early 2007 and much much worse.
So here is the question from my friends/clients, "my parents want to move here to Austin because of the grandchildren in Texas (two sets) but their home has lost it value. If they were to sell it would be a 'short sell'. Even though their credit is above 800 they might want to go ahead and take the proverbial hit. They have been waiting for over 4 years to do this and nothing seems to be improving. They attempted to sell 2 years ago with zero results. What will this do to their credit if they attempt the short sell?".
I called a lender for some feedback on this question. First, a mortgage payment(s) needs to be missed. Then the process can begin since a mortgage company sees no reason to accept less than what is owed if all payments are being made. And there is no guarantee the bank will accept a 'short sell' in any event. The real question is what will this short sell to do a 800+ credit score? The answer is an estimate due to all the variables but in short, it will drop it to low 600's or 500's quickly.