From the moment it was announced, Robbie Amell's return to The Flash was something that fans of The CW series were very excited about. After all, while his character Ronnie Raymond's time had been brief, his lasting impact as one of the original halves of Firestorm as well as the love of Caitlin Snow's (Danielle Panabaker) life remained. Ronnie had sacrificed himself to save Central City and Caitlin had never really gotten over the loss of her husband. However, by the end of "Resurrection" the excitement for Ronnie's return had turned to horror as it was revealed that Ronnie really was gone. Instead, the entity Team Flash had been dealing with as the Black Flame and that Caitlin had "resurrected" is actually Deathstorm and now the terrifying entity is free to cause even more chaos and harm. But while Deathstorm is terrifying in his own right, the reveal of the character had many fans wondering if The Flash was setting the groundwork for a larger story, one that could serve as a perfect ending for the idea of the Arrowverse as we know it: Blackest Night.
For those unfamiliar, Blackest Night was a 2009-2010 crossover storyline written by Geoff Johns with art by Ivan Reis. The comic story saw members of the Green Lantern Corps – and as the story progressed, much of the rest of the DC universe – face off with Nekron, a personified force of death seeking to eliminate all life and emotion from the universe. To do this, Nekron had an army of previously dead superheroes and even those who had died and already returned to life, turning them into his Black Lanterns Corps in the process, a roster that ended up including some major heroes. In the end, the good guys prevailed and 12 of the Black Lanterns were returned to life for follow up series (Brightest Day) that explored their journeys, but the general aftermath of Blackest Night changed the rest of the DC universe. Characters found themselves set on different paths, and notably for Flash, the resurrection of Reverse-Flash set up his role in The Flash: Rebirth which in turn had major impact on the DCU via Flashpoint.
Adapting Blackest Night for The Flash wouldn't necessarily be a direct lift from comics; after all, John Diggle's (David Ramsey) Green Lantern storyline hasn't fully come to fruition and some of the other major players within the comic storyline aren't characters that we would expect to see in the Arrowverse. That said, the general concept could loosely work, both as a devastating event for the end of Season 8 of The Flash — something that showrunner Eric Wallace has already teased — and as a larger issue for the remaining Arrowverse heroes to take on next television cycle.
Right now, only two Arrowverse shows have been renewed for the 2022-2023 television season: The Flash and Superman & Lois. The other series, DC's Legends of Tomorrow and Batwoman, have not yet been renewed. If those two series do not get picked up, adapting Blackest Night/Brightest Day would offer an opportunity to conclude their stories in a sense, possibly conclude The Flash, and set Superman & Lois up to continue alone as part of the aftermath. It's an avenue that would allow characters from non-renewed shows to appear crossover style (akin to what we saw with "Armageddon" this season on The Flash). Depending on how the story would be plotted, the end could see the restoration of beloved heroes essentially riding off into the sunset to serve their communities or could even trigger events to where the Arrowverse multiverse would open back up, allowing for shows to separate themselves out again, thus allowing Superman & Lois to continue independently from the rest of the Arrowverse. That itself would give the network something of a "clean slate" as it continues with additional DC inspired programming, such as Gotham Knights which isn't connected to the Arrowverse and Justice U which is.
Ultimately, an Arrowverse take on Blackest Night and its follow up Brightest Day feels like a good fit for The CW's shared DC universe. With it increasingly seeming like the Arrowverse is coming to an end combined with The Flash setting up for this horror-based storyline, taking on Blackest Night would offer one more major event to bring the Arrowverse's heroes – past and present -- together before passing the torch to new stories, new characters, new shows, and whatever the future holds.