I suspect the next step the state will do is announce a week-long “amnesty” for those flouting the law to come forth and comply with the registration requirement. That will have essentially the same level of failure as the law’s initial deadline. Even in states like CT, some folks know unconstitutionality when they see it.
Further, that 300,000 estimate doesn’t include the supportive family members of those refusing to register.
They already gave “amnesty” for a month or so. I think the amnesty period is over. And as you suggested, I’m pretty sure that failed also. The way I see it, their only remaining options are concede defeat before burying thousands of gun owners and SWAT team members, or bury thousands and then concede defeat. The former would probably be less expensive.