Well, if you had a weather radar but got struck by lightning anyway then the weather radar wasn't doing you much good was it? You may as well have had it off in the first place.
To me this is a question about a scenario that is unlikely enough that I wouldn't lose too much sleep over it, and if it did happen I'd just play it by ear. Do I think I can transit the weather safely using visual techniques or help from another aircraft? If not, go land somewhere and have the thing fixed.