There has to be a reason he's dying, but whether the story will dwell on the specifics is up in the air. But with the prominent Borg storyline this season in conjunction with Q facing death, I can't help but wonder if all this somehow has something to do with the episode Q Who? It's a reach, but if you look back at all his appearances on TNG, this was the only one that fundamentally altered things. In Encounter At Farpoint he just held the Enterprise up for a bit, and then spent time trying to goad Picard along one way or another. Then he briefly gave Riker powers to try and teach Picard somethingorother, but then he showed up and flung the Enterprise across the galaxy and gave humanity a premature encounter with the Borg. Very notably, this was NOT undone at the end of the episode like every other Q encounter, the episode ends with the Borg heading to the Alpha Quadrant as a result of the encounter. At most Q's other appearances came with a lesson for Picard specifically, but this was the only one that actually changed things on a galactic level.
Pair this with his reaction in Voyager when his son messed with the Collective ("Don't. Provoke. The Borg!") suggests that there's something about them even the Continuum doesn't want to or otherwise can't get involved with. And what else happens in Voyager? The evident death knell of the collective as we all know it, the Borg never really recovered from that event, and it's something that likely would not have happened were it not for Q introducing the Federation to the Borg before it would have otherwise naturally occurred. Think about it, how likely is it that Voyager would have survived encountering the Borg in the Delta Quadrant if they weren't already forewarned about them thanks to Q? No first encounter with the Borg, no Wolf 359, no development of defensive strategies against them, no chance Voyager survives their first encounter. And thus, no future Janeway to deal a crippling blow.
Now, I'm not sure how all this translates to Q dying, and its entirely likely I'm overthinking things and the actual answer will be much subtler. But between the prominence of the Borg this season, the Janeway namedrop this episode, and the fact that it's all the result of the ONE thing Q did that had lasting ramifications beyond Picard himself just makes me think these are the proverbial chickens coming home to roost for him, somehow.