The radar could quit due to the inherent frailties of electronics.
A lightning strike can knock it out.
I have seen photos of big iron with the nose cone blown off by radar.
Above is a photo of hail damage to a radar cone. A radome can be destroyed by hail. Also, it is possible to damage the cone enough to reduce the efficiency.
Apparently they had a major electrical failure. That would require all unnecessary equipment to be taken off line. Whereas radar might be considered necessary, it does rate below the flight instruments and the flight controls.
But I would bet that whatever got the electrical system got the radar at the same time and they had no choice.
I wish some high altitude big iron driver would comment, but until one does:
In my case, I had a radar with 160 nautical mile range.
The typical scenario where I got more than I wanted in weather was like so:
I knew there was heavy rain. But no TBZ near the departure airport, so off I go.
As the trip progresses, I see quite a bit of precip, and some fairly large areas of red, but they are not of the shape that indicates a thunderstorm. Just heavy rain. And I can see that the weather goes to yellow and then green beyond the red, so here we go.
As I get into the red area, the radar shows that about 40 Knm ahead, the precip ends. So press on.
After another 20 miles or so, I see that the radar is still indicating the end of the rain 40 miles ahead. Aha! Attenuation. It is raining so hard that 40 miles is all I am going to see.
At 180 knots, that gives me only 13 minutes to identify my best route, communicate with ATC and get a permission to deviate and of course, not seeing any further, there is the worry that there may be a worse area in the selected direction.
Big iron has better radar than I had. But at their speeds it is all relative.
I am only making the point that as wonderful as airborne radar is, it is not infallible.