“...static mode...”
Interesting. On the press conference one of the guys said how (IIRC) there are no “consumables” that give it a limited lifespan. But wear and tear on mechanical parts exposed to the elements. (I thought of axles, etc.) So perhaps you are correct that it may lose mobility, but still be able to do something. Although I imagine it would get pretty bored sampling the same rock over and over again. ;)
The guy said they did mechanical and environmental stress tests on the rover to a certain level, and he said it is designed to last two years. However, he said that no one would be surprised if it lasted for four years and beyond.
Considering the mobile longevity of the previous rovers, I believe electrical, not mechanical will be the factor involved.
They do design rather well, but, there is always a shelf life on power.