What does your organization consider a RISK Factor?
Was the use of an outside contractor considered a RISK Factor when it was being considered?
Does the Scrum Team understand the requirements as stated?
How likely are these requirements to change?
Is it known who that individual contacted to gather the requirements so that those individuals are known stakeholders to be involved in Sprint Reviews?
Will the Product Owner now be the one to maintain those relationships?
Will any of these requirements actually be implemented?
This is the definition given by Merriam-Webster
Definition of risk factor
: something that increases risk or susceptibility
Is that a reality of the contractor leaving