To delete a client record, everything throughout the database that has referenced that client would need to be removed, Notebook entries etc included.
It may be best to Create an Archive sector and place the record in there to store it separate and out of sight of the rest of your database and records.
Our support team might be able to provide some guidance of approximately where a link could be, but they will not be able to remove the link for you.
Some links can only be removed through our professional services team which will include an additional cost - please speak to your Customer Success Manager or Account Manager if this would be of interest to you.