Some buyers think the HOA needs to be 100% funded, which is never the case. Still...it is their right to cancel based on that criteria.
If your property still qualifies for FHA financing, meeting FHA guidelines for Reserves, then not likely. If your property was qualified under FHA guidelines at the time the buyer made the offer, but later and during escrow lost that status, could be another story.
If your agent noted in the mls that buyers could purchase FHA, and that turned out not to be the case, then the buyer might be able to sue you for monies he may have expended pursuing a purchase via an FHA loan based on erroneous information.
Funny thing about suing people...sometimes they counter sue as a result and you lose not only your case but the counter suit. If the buyer could not get financing due to the insufficient reserves or some other reason like a pending lawsuit, and that was not disclosed, he might want you to reimburse him for his home inspection, as example.