It is very difficult to diagnose a problem from a photo.  There are so many factors that come into play when we see a photo of a distressed plant:  what was the weather the preceding fall and summer, were there any periods of drought at that time, any new chemicals used in the area or by neighbors, how long has it looked bad, etc.  Rhododendrons do have a finite lifespan and yours could be reaching the end of it.  I lost a number of plants this year due to the prolonged drought and heat that some parts of the Piedmont had last summer.  Some were native to the property such as a very tough wax myrtle.  Rhodos also are susceptible to root rot and fungal diseases, especially if stressed.  I would recommend that you continue to monitor the plant and if you see no new growth in the spring, then take a sample into your local extension agent or Extension Master Gardener Office.