Contract for Term Employee

Hi there,
Now that the laws have changed regarding the length of time someone can take maternity/parental leave, do you have any recommendations on whether you can include a clause in a term employees contract that states you can terminate the employment relationship if the employee comes back from leave early?

As an example, if someone says they are going on leave for 18 months, but decides to come back after 13, then do we still have to keep the term employee until 18 months? My understanding of term positions has always been that if you want them to leave before the term is up, you have to pay them until the end of the term. But if we can add a clause this would be helpful. If you happen to have any resources on this that would be great. If it it something we could do I would contact a lawyer to draft specific wording. Thanks