There is way too much speculation and way too little information to give rational advice on the subject.
1. First off the sellers were ok with an FHA mortgage, first red flag for an "as is" sale. FHA mortgages are and can be very restrictive to property condition. I was an agent in an affluent area of the country who represented homeowners, it was very rare my homeowners would accept an offer with FHA financing.
2. I dont see how the buyers can lose their downpayment. Mortgage contingency is common, if the bank will not write a mortgage buyers get their downpayment back, simple stuff. Doesnt matter if it is "as is" sale or not. Actually all sales are "as is" in the strict sense of the word. Though most contracts give a time frame to have a professional inspect the property AND a mortgage contingency. Unless for some silly reason buyers did not hire a lawyer and allowed the mortgage contingency to be stricken from the contract. IF this is the case, this is the buyers negligence.
3. There is more to this story, there has to be because this deal can not be posted with just a few lines. Clearly the sellers may have other offers or realized they can get more money based on the OP post that the house was a great deal. That would explain their reluctance to move ahead with the sale, clearly their right.
4. Typically what would happen with a headstrong seller in this case and if the buyers wanted the house. The buyers would pay to upgrade that breaker panel at their expense by reimbursing the seller at closing or addendum to the contract to upgrade it. If the sellers do not want too, then clearly they have no motivation to sell the house to the buyers. If the buyers can't afford to give them the money, then clearly they cant buy the "as is" house. Dead house deal, buyers get their downpayment back, move on.