To be honest there's only a 50-50 chance the short sale will even go through at least half the time the Seller doesn't qualify or there are multiple line holders on the property and if one of them refuses to accept the deal then the sale doesn't go through. So you're a back up on what is already a shaky deal at best.
Inquiring about their desired procedure at this point may clear the way for you to take future action without involving the expense of an attorney. As always, having things in writing is advisable.
Sometimes a back-up offer has been negotiated with the seller, executed (signed-off), earnest money deposited, contingency deadlines and a "cancellation of prior contract" clause initialed. Then there are back-up offers that haven't been executed.
Please make sure your are not legally obligated to the contract prior to putting in an offer on another property.