In a short sale, the homeowners (sellers) can accept your offer...but that does not mean the offer will be accepted, much less approved by the sellers' lenders in a short sale. Yes, the horror stories are there where buyers and sellers wait and wait and wait, only to be told that the lenders will not approve a short sale.
That's why, in the state of California, we have a short sale addendum wherein we specify that the buyer's offer is good through a certain period of time, that the escrow isn't opened until formal acceptance (in writing) by the short sale lenders, and that the buyer's initial deposit will not be cashed until receipt of such approval.
Until the offer is accepted/approved by the short sale lenders, there's no guarantee the sale will move forward. A short sale is made doubly harder and more challenging when there is more than one loan, and when there is more than one lender.
So yes, the buyer should explore other avenues and look at other properties to buy just in case. As such, the buyer may write an offer on another property.
If, however, that short sale is ratified by the short sale lender within the time specified by the buyer, the buyer should do the right thing: if the buyer is no longer interested in the property, or if the buyer has an accepted offer on another property, the buyer should officially withdraw his offer.
Throughout the process, your agent should follow up with the listing agent(s) to find out the status of your offer(s).