My doubts about Seven of Nine faded quickly, because a single episode—Star Trek: Voyager season 4, episode 2, "The Gift"—proved that Jeri Ryan wasn't only there to boost Voyager's ratings as a sex symbol. Instead, Seven's appearance in "The Gift" was almost grotesque; and Ryan's performance was raw and desperate. Seven of Nine rescued Voyager from the ratings heap not just because Ryan was gorgeous, but because Seven of Nine's character arc explored the essential Star Trek theme of what makes us human. So what would Star Trek be like now if Seven of Nine never joined Star Trek: Voyager?
Star Trek: Voyager Without Seven Of Nine Is Hard To Imagine
Star Trek: Voyager Could Have Been More Stagnant—Or Much Darker
It's hard to imagine Star Trek: Voyager without Seven of Nine, but Voyager's last four seasons might have been more stagnant without Jeri Ryan being added to the Voyager cast. Kes would still have left, but without Seven replacing Kes, the Doctor's (Robert Picardo) character growth might have stalled without anyone to learn from or teach. Few others on the USS Voyager were as willing to risk conflict with Captain Janeway as Seven was, so Janeway's character development might also have stagnated. And without Seven aboard, the Borg Queen probably wouldn't have become one of Janeway's greatest enemies.
If Star Trek: Voyager reached seven seasons like Star Trek: The Next Generation and Star Trek: Deep Space Nine, Voyager's ratings would have continued to drop without a renewed focus. If that wasn't Seven of Nine, season 4's "Year of Hell" might have covered an entire season instead of being reduced to a 2-part Star Trek: Voyager episode. Star Trek: Voyager would have been a lot darker and more desperate. That worked for DS9, but making Voyager just as dark as the Dominion War would have steered the Star Trek franchise away from its optimistic roots—maybe for good.
No Seven Of Nine Would Have Totally Changed Star Trek: Picard
Seven Of Nine Understood Admiral Picard's Borg Trauma
Despite appearing in only three episodes of Star Trek: Picard season 1, Seven of Nine had a major impact on Admiral Jean-Luc Picard's (Patrick Stewart) continuing story. Before the USS Voyager's 2378 homecoming, Picard's ordeal as Locutus in Star Trek: The Next Generation was the only exception to Borg assimilation being a death sentence. But because Seven was a former drone who had been assimilated as a child and still fully reclaimed her humanity, it was possible for other Borg drones to be saved, too. Without Seven, the Borg Reclamation Project in Picard's first season may not have existed at all.
Star Trek: Picard's Borg Reclamation Project allowed Star Trek: The Next Generation's Hugh (Jonathan Del Arco) to return to Star Trek as a fully liberated drone, even if Hugh's return was too brief.
Star Trek: Picard season 3 would also have been radically different without Seven of Nine playing pivotal roles in Starfleet's ultimate victory against the Borg. A new character on the USS Titan-A might have helped enact Admiral Picard's plan—first taking the Titan where it's needed, and ultimately rallying the remaining crew members to defeat the Changeling-Borg Alliance. While Picard also dealt with Borg-inflicted trauma, the Borg ruined Seven's entire life: stealing her childhood and marking her as different, even after being liberated. A different character in place of Commander Seven of Nine wouldn't have the same emotional impact.
Star Trek Needed Seven Of Nine & Would Be Lesser Without Her
Seven Of Nine Influenced Star Trek After Voyager
Star Trek would have been radically different after Star Trek: Voyager without Seven of Nine, and I'd argue the franchise would have actually been much lesser. There's no doubt Seven of Nine helped raise Star Trek: Voyager's ratings, so Voyager might not have run for a full seven seasons without Seven of Nine. If interest in Star Trek: Voyager waned enough to justify an early cancelation, we probably wouldn't have gotten Star Trek: Enterprise. And if we did, Subcommander T'Pol (Jolene Blalock) would have been different without the template that Seven created.