Romney would replace Obamacare with a law that would require insurers to do what they were already doing before Obamacare, but makes it sound better than it is:
The key phrase here is "continuously insured."
As pointed out by Jonathan Cohn via Think Progress:
the federal government already forbids insurers from denying coverage to the continuously covered through the 1996 Health Insurance Portability and Accountability Act (HIPAA). But the measure has been seen as a failure because “there is no limit on what insurers can charge under HIPAA” and the law does “little to regulate the content of coverage, leaving the door open to insurers to offer bare-bones policies. In addition, HIPAA notice requirements are weak, making it hard for people to know about this protection.”