The Falcon, and most ships of it's era going forward have more than 1 hyperdrive. A 'spare tire" secondary that's incredibly slower than the primary. Limited range and slow. And I assume there is some switch over time, or everytime the main drive didn't engage, they'd have just switched over to the backup and been away. Check both the wookieepedia entries on hyperdrive and Millennium Falcon. Has everything needed to cap the discussion.