It might be possible to use the remaining electrical heaters as some kind of crude thermal battery (assuming they have any heaters still running, they already shut down the heaters for most of the scientific experiments).

Simply turn the heaters off before transmitting and keep any transmission periods short enough that the electronics don't get too cold.

JPL probably have a bunch of tricks like this ready for when power levels drop. That 2025 estimate is 10 years old and I'd be surprised if it's final.