GIven that your offer is only good for 4 days, you can move on whenever you'd like and find a different home.
I usually counsel my buyers that when dealing with a short sale they shouldn't hold up their search waiting on it. If it comes through, great. If not, you keep moving anyway to find another home. You don't have to put any earnest money down with a short sale (at least not until the lender approves the deal), so you should keep your options open and keep looking.
If you get it, great - if not, hopefully you didn't put all of your eggs into that basket.