If the tenants chose to leave, there is nothing you can do to stop them. However, if they move out, they are breaking the contract.  Once you have confirmation that they are leaving, you must try to re-rent the unit as soon as possible. They also have the right to assign their lease to someone else with your approval.  For more information on assignment of tenancy please refer to the our Fact Sheet on this issue,  https://landlordselfhelp.com/media/Subletting-and-Assignment.pdf.