I have a feeling he will end 1 more year at #1 at some point, but that is it. It will be difficult for him getting back to #1 because:
1. His own slight decline and Djokovic's improvements mean Djokovic has surpassed him in current ability. I still think a healthy and in form Nadal will beat Djokovic on clay or grass more often than not, but 70% of the tour is hard courts anyway, and at this point Djokovic has the edge there. I dont believe Murray has surpassed a healthy Nadal in ability yet, but he too could reach that point, and likely will at some point with continued improvement and Nadal's likely continued decline. Murray is only 1 year younger but is obviously following a different career path.
2. He will find it harder to stay healthy for a whole year. I do think this year could have been a chance to return to #1, or atleast before the nightmarish Wimbledon, but then he gets injured and missed half the year, and almost falls to #5 as a result. He has always been more of an injury risk than most, but that is probably even stronger now.