Provided he hasn't been given any notice to end the tenancy, if no changes have been made and no new tenancy has been granted then your friends's tenancy will have statutory protection.
They cannot be evicted in the first period of the tenancy eg 6 months unless they have broken the agreement eg unpaid rent.
It's called holding over, the tenancy continues on the basis of the current tenancy.
Notice can differ, normally 2 months from a normal start date of a tenancy (usually the date signed or rent date).
So if the tenancy started on the 1st Jan and notice was served on the 2nd Jan the tenant should have until the 1st April.