A Center Controller reported an aircraft temporarily lost control after being struck by lightning. The Controller was unable to communicate with the aircraft due to their frequency transmitter site failing.

Narrative

This aircraft was climbing up the hill" out of ZZZ approach through moderate weather. The weather was called to the pilot and he was told that if he needed to deviate he could; but it would need to be a right deviation to avoid the military airspace. He didn't indicate that a deviation would be needed and proceeded to climb. Many other aircraft had also transitioned through this weather; which was predominately moderate precipitation with some small areas of heavy precipitation about 25 miles wide in total. On the far eastern edge of the weather; roughly 20 miles south of the ZZZ VOR I observed the aircraft make an incredibly sharp turn from a heading of roughly 040 to 120. I also saw that his altitude had begun to drop very fast; even though he was still supposed to be climbing to 23000 ft. I made multiple transmissions to try and reach the pilot without any response. Then we heard the pilot radio over the guard frequency. I transmitted on guard and still got no response. Over the course of the next few minutes I made at least a dozen transmissions to the aircraft without any acknowledgement. Then controllers; who were training on Sector XX; transmitted on guard and the pilot heard them. It turns out that the aircraft had been struck by lightning and briefly lost control of the aircraft along with all instrumentation. A minute later and he was back in communications with me on my sector's alternate frequency XXX.XX. He leveled off and regained instrumentation and advised that he wanted to return to ZZZ to land. After a short conversation I encourage him to go to ZZZ1 instead; which avoided needing to turn around and fly back through the weather. For months upon months we have had trouble with the transmitter site located at ZZZ. This aircraft was high enough that communications should not have been an issue on XXX.XY; but I couldn't reach the pilot at all on that frequency or through XXX.XZ. We have dead zones where for no explainable reason we just won't be able to reach aircraft in places that never used to be an issue. I've worked as a controller on these sectors for more than five years and the reliability of our radios on this sector are at an all time low. Whenever we report issues about these sites we are told they will be reset; or a storm is causing the outages; or to log our issues over the course of the shift and they will look into it. But it all feels like it goes nowhere. This has been ongoing for months with no resolution and today a pilot could have died because we couldn't communicate with him effectively during an [urgent incident]. Reliable communication is one of the most important tools for us to do our jobs effectively and I don't know anyone in the area who would use the word reliable to describe the state of our radio sites on this sector. We need our transmitter sites to work more reliably at ZZZ. Maybe this requires new hardware and needs to go above and beyond remotely resetting the site or messing with Diversity Algorithms; backups and standbys hoping that some magic combination will yield passable results for a few hours. We should be able to count on our main transmitter to work the vast majority of the time."