I haven't had a situation where the seller failed to close,however the NC Offer to Purchase and Contract is extremely clear that should the seller default they are responsible to return not only the diligence fee but in addition all documented expenses the buyer incurred (mortgage application fee, appraisal fee, inspection fees) If you and/or your buyer broker are having a tough time in getting the seller to return your money after they have failed to close by day 15 after the listed closing date, then you should have your attorney contact them.
I've just read your reply to Michael below. and while the seller seems to have been less than honest and perhaps unethical in not disclosing structural issues you feel they knew about, this isn't a seller breach or contract. Honestly Seller Property Disclosures are and have always been worthless pieces of paper and why their mandated is beyond me. Let's be honest, if the Government wanted sellers to honestly disclosure then the form would be binding (it's not) and there would be no option for a seller to essentially "take the 5th" by choosing to check "No Representation" Buyers should simply sign the mandated form and forget about it. Buyers have the right and responsibility to do their own diligence. That's why you have inspections done. Regardless of the problem I have more than enough experience to say with confidence any issue can be repaired it's only money. Have you had a structural engineer evaluate the problem and recommend a repair? Have you had a qualified contractor then come in to quote the needed repair and presented this information to the Seller and request they cover the repair?
While perhaps you should not have offered $1000 in diligence (again I don't know all the circumstances) and while I'm not certain if these issues could not have been somewhat obvious if not to you then to your buyer broker, from what you've written there is no failure by the seller to perform, just a failure of the seller to be honest when filing out the seller property disclosure which as I've already indicated has never been a binding document.