"Mr. Data, lay in a course for the 24th century. I suspect our future is there waiting for us."
"Course laid in, sir."
"Make it so."
Because they figured out how the Borg jumped through time.
And considering how many means of time travel there are, from the Borg's temporal whatever to the chrono deflector for the Klingons in "Endgame" (VOY), it kinda makes the old slingshot rather redundant.