I wonder if you could do a hybrid approach, where the nuclear device is very small, but able to charge the battery over a longer duration to the point where the solar panels can be repositioned and utilized again.
Lots of missions use radioisotopic heaters, where you don't bother with the thermocouples and just have the material get warm and protect components which are vulnerable to low temperatures.
That's the main reason why spacecraft don't survive a temporary power outage: terrible environmentals.
But at this point, we don't have a lot of Pu-238, which is one of the only decent candidates.
