In a way, yes, but in another way, no.So... if Picard and the E-E weren't there, even if the fleet defeated the Cube, the Borg would still win.
From what we've seen, time travel seems to create an alternate universe for your changes to exist in, rather than changing the universe you were originaly in. It would explain why we've never seen any Grandfather Paradoxes in Trek, and why "our" timeline never seems to be affected by any time travel f*ck-ups