Judging from s3, I think Voyager without Seven would have lasted maybe 5s before they pulled the plug if they didn't use another "Jump the Shark" stunt to boost ratings like kill off a character or a wedding.
They could have ended Season 3 with the ship in the midst of a hopeless battle, the characters rushing to the escape pods, then have a massive explosion, leaving it a mystery for who would survive.
At the beginning of Season 4, the battered and bruised Equinox
discovers the remains and starts saving escape pods, only to reveal who had survived and would blend in with new characters and a new ship.
How's that for a shake up?