Oludeniz is really dead in winter, there is one bar open on the sea front. Also Hisarönü is sort of deserted, only a few restaurants are open for the expats living there.
On the other hand Kayaköy and Fethiye are as lively as always, less tourists of course. Busses to Kayaköy drive every once an hour from Fhetiye, to Oludeniz probably less than in summer but they do drive.
By the way the beach on the sunny day is winter is perfect!
Have a look:
As long as the weather is sunny the days are perfect for exploring. Today it is raining, but I have seen Christmas here sunny, a bit chilly but lovely!