Star Trek: 10 Secrets Of The Q Continuum
2. They Aren't Immortal After All
When it was revealed that Q was dying in the second season of Star Trek: Picard, Q seemed just as surprised as the fans were. As we mentioned earlier, members of the Continuum have always been able to kill each other, but no one knew they could also die by seemingly natural causes. They have always claimed to be immortal.
The reason for Q's death was left unexplained. He stated that he was 'on the threshold of the unknowable' and about to be 'enveloped in the warm glow of meaning'. He began to slowly lose his powers, and used his remaining energy to return Picard and the others to their own time period.
Given how reluctant the Continuum was to allow Quinn to die, the revelation that Qs can die of purely natural causes must have had drastic implications for their society. Perhaps this was a new stage in their evolution, similar to the 'new era' that Quinn described.
It's also likely that other members of the Continuum may have started to die off after Q, which could explain why they stopped visiting Starfleet after the 26th century. Of course, they could repopulate by creating a new generation (much in the same way that Q Junior was created), but this would still cause severe changes in their society. Another possible explanation is that the Continuum was killing Q as punishment for his rebellious behaviour. Q rebelled against his species on several occasions. Once, they punished him by turning him into a Human, so killing him doesn't seem that unlikely.