OneMoreForExtra CONGRATULATIONS on the prospect of a match. Great news after waiting so long. 
In your shoes I would not want to do anything at all to jeopardize anything to do with the adoption. So if you do hassle/encourage your social worker I'd make sure they knew it was because I was so keen to adopt and not because I needed to tell my employer anything.
Can I ask - does your employer know you are planning to adopt? Assuming they do, they should know that a match could come at any time and could fall through at any time too. So if you have made them aware of the situation, which I think is only fair, then you've told them. If not, they should know this, IMHO.
That said, if they know you are planning on adopting I don't think you are under any obligation to tell them 'full disclosure' because you simply do not know what will happen yet.
If you can afford to not work and do not want to work then I would say go for the redundancy, if that is what you want, and make it clear to your employer you would be keen on this if offered.
Likewise, if you do not like your place of work, at all, and there are no jobs there you would want to do, I would also, probably, go for the redundancy.
I often used to fantasize about being a stay at home mum, but we could not afford it! Now, 18 months after returning to my part time job, I am actually quite happy (but it did take me a full year to get back into it after a year off!).
So if work is something you want to avoid and can afford to avoid, or the workplace if not a good place to be, go for redundancy.
However, if you would need to return to work post adoption I would be very cautious about leaving a job or making it easy for them to let you leave. This is because it is sometimes (I would say most often) easier to negotiate a good part-time package in a job you like (or as a job share) from a position of doing that job already (even if you are currently full time), than to simply go and look for a part time role in your chosen job.
I think as an existing employee you may get to negotiate days and times in a way you would not by walking into a new job as a mum.
So I would go for A, get the best possible next job you can and if/when you need to leave, leave for the full amount of time you want to take and return to your job. I found returning to a job I knew or at least a place I knew (I seemed to have forgotten a lot!) was much easier after our adoption - as opposed to returning to work after our birth daughter where I had to a take a less interesting/less fun part-time job having left my full time job when I was not offered the chance to do that job part time.
I do hope that all makes sense! Message me if it does not.
And if you are the kind of person who really needs to know all the facts before a meeting then do delay the meeting but remember you may still not have all the facts when you meet and delaying might then not be in your best interests if it means missing a good work opportunity! I know your head will not be in 'work' but if you will need to return to work i a year you do need to think what would best accommodate working and being a new mum.