How about spend the last afternoon sitting at Sundowners pondering why you would ever leave this place (and buying the off-duty divemasters drinks). When the sun goes down, get some food at one of the local places, and head on over to the Purple Turtle. With any luck you will be unable to make your morning flight but will recover in time for an afternoon dive.
Roatan is not a topside town, except in the benefit of socializing. Find a quiet stretch of beach or iron shore and read a good book while sipping some rum or Port Royal.
Also - Dian's Garden of Eat'n is still open. It is, in my humble opinion, quite pricey for Roatan. The food is good, but my wife and I were not overly impressed in comparison to many of the other places we went to on our last two trips. The prices range from 250L - ~300L (18.5L = $1), which by Roatan standards is a kings ransom. The filet mignon at Argentinian is 240L, compared to the rather paltry portion of red curry chicken at Dian's for 250L. Perhaps we ordered the wrong meals, but I felt that Dian's was more about atmosphere and the sense of a "nice restaraunt" than it was about a good dinner. Lastly, if you decide to walk it, be warned that there are very limited street lights between Dian's and West End - it's a 10 - 15 minute walk in complete darkness. Great chance to view the stars, but try to avoid the maniacs driving along at 50kmph.