In many cases, things like compensation for pain and suffering are allowed rto be retained. However critical illness compensation is a different animal, for different purposes and it will depend upon what it is to be used for as well as the opinion of your IP.
It could well be that, as a F&F offer has been accepted and paid he / she will decide that it is yours, but F&F seldom means what we think it means as the wording of these things differ from case to case.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk