100% of nothing is still nothing.
If you readvertise you'll probably get less, and even if still interested, if it doesn't sell your orignal buyer will offer you less if they come back at a later date aswell.
So your choice is hold out and possibly not sell. Or drop your asking. IMO its a falling market and buyers are prepared to wait. If you drop your asking and your original buyer does the same maybe they'll move their property. But you'll have lost out, and they won't. At the right place anything will sell. It depends on how long your are prepared to wait and low you are prepared to drop to. After 5 months I wouldn't wait for the original buyer I'd put it back on the market. Theres still a chance someone else will offer the asking, or close to it.