I do a lot of short sales and I would tell you to be prepared to wait up to four months or more to get an answer. It has less to do with who the bank is sometimes and more to do with the other details of the sale. Meaning, how many banks are involved is there a second mortgage you are not aware of? The other piece would be how much information does the bank already have from the listing agent? Have they already submitted all of their financials, hardship letter, budget plus the making homes affordable package? If all of these forms are not already with the bank at the time he wrote the offer it can delay the decision by the bank by several months. Have they had a BPO? What has the listing agent told your agent regarding where they are in the process?
If you really like the house will be worth the wait but you have to be willing to be patient. That's the key to short sales. If you want to get a deal you have to be able to wait it out.
The answer is "Yes", as they are not able to get clear marketable title. I have been in this situation numerous times, and if you can hang in there until they get marketable title (may take 3-6 months...or more), it may be well worth it. If you can be in contact with the attorney/paralegal that is representing the bank, you may be able to get a lot more information. There will be more than adequate language in the purchase agreement that protects them from performing, so your best bet is to concentrate your efforts on figuring out the time-line and the specifics to close.