It makes no sense for Picard to evacuate the crew (what little was left by that point - if the Borg had assimilated up to deck 6 as we're told, likely only a small portion of the crew remained) to Earth with a reminder to "keep out of history's way." No matter what, they were going to change history. And very likely their future would NOT have been waiting for them.

What with the "temporal prime directive" etc, they should have just blown up the ship with everyone who was left still aboard, or - if they had been able to do so - take the ship somewhere else before blowing it up so that there wouldn't even be starship fragments in orbit or landing on Earth to mess things up.