In this market, if you have a real estate agent that is familiar with short sales, like me, there really shouldn't be a lot of reasons WHY your home would not sell in a short sale position. (unless you have a lot of assest or cash in the bank, or falsified loan documents, the bank will negotiate).
To answer the bottom half of your question, you until it sells on the courthouse steps and or the bank has served you eviction / vacate demand from the courts delivered by a process server (normally a deputy).
Hopefully your agent prepared you to save $ because if you are renting a place, chances are they will ask for 1st, last, and a security deposit, and you will still have to undergo the application process.
If I can help or answer more questions let me know.