Hi OP. I'm a social worker fwiw (child protection and CIN). Sorry you've had the experiences you've had. If you've had lots f changes of worker it sounds like you're in an area where children's services are in crisis - when that happens workers come and go because the job is unmanageable and you get drift and delay. Unfortunately, as CIN cases are usually held within teams that also deal with child protection, Child protection naturally gets prioritised above CIN. If the social workers caseloads are so full of CP work they're not going to get round to doing a risk assessment for CIN. Not saying it's ok but it's what happens in reality.
First of all, as others have said CIN is voluntary. You can ask for your child's case to be closed. CP shouldn't be used as a threat to keep a case open - if there was enough evidence of risk for it to be CP the worker should have taken it to conference already. Yes you do get some arsey workers who forget that families have rights to say no but if that happens take it to the team manager, Iv yet to see a family stay open on CIN if they have insisted they want no input. I do get what others are saying about lack of engagement, but you have engaged! that would be more of a worry at the start of a case. For example, say a family were referred in for possible neglect and a few missed health appointments, it starts as CIN and then the family won't let SS through the door or see the kids, thats starting to head towards CP if the worries continue.
If there was a longstanding issue that a social worker felt was very likely to get worse, they could warn you that ending CIN prematurely could end up with you being referred back and on CP in future. HOWEVER I'm not sure of the likelihood of this from what you describe, given that it doesn't sound like you're getting much support from the service, so I'm not convinced that taking it away is going to mean a negative impact for your child/children. An example of this would be where SS and family support workers are providing a lot of practical support and we can see that a parent is likely to struggle once that is taken away and that it could well become a safeguarding issue for the kids.
Re the risk assessment - I genuinely can't tell from what's been said whether this is a procedural thing (a SW wanting to check a new introduction to the family, which wouldn't have occurred if the family didn't happen to be known by CS at the time) OR whether there is info that suggests he is a risk. What id be wary of is whether 'do a risk assessment' has been carried over as a task without the new social workers scrutinising the relevance. It certainly feels oppressive to me to ban someone from having unsupervised contact for that long without giving reason. In fact, I can't see that there would be any legal basis for doing so, though I appreciate that advice from SS whilst not legally binding, carries a lot of weight because of the power they potentially hold.
I'd recommend: contact the police and request info under Claire's law and Sarah's law - this will tell you if there are any known concerns re domestic abuse or offences against children, which would be two key things that may have shown on a police check (though be aware that other things eg organised crime/drugs wouldn't be shared under these)
Ask for an appointment with the team manager about the RA and when you see them, ask for their view re any potential risk to the child. Ask about their view re case closure and what any potential consequences of this would be.
If you trust your partner, take him with you to the meeting. They can't tell you about information they hold on him, but they can tell him, and discuss with him whether they can tell you with him present. I've had this work when for example someone has something in their history and they've been happy to share it to dispel rumours.
Oh and last point - be persistent about asking to meet with the team manager or practice supervisor (check that the person you're meeting is the person who supervises your child's social worker, as the level that will be can vary) Don't think you're being fobbed off if you struggle to get them on the phone just keep trying. I know that my manager spends her days chairing meetings back to back and people never believe us that they literally are at their desk for probably less than 30mins a day!