All perfect praise be to Allah The Lord of the Worlds and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The person who joins the prayer late shouldn`t walk to a nearby Sutrah(an object placed in front of the praying person to prevent people from walking within his praying area) after the Imam makes Tasleem(At the end of the prayer) since the Sutrah is Mustahabb(Recommended) according to the majority of the Fuqaha, and not obligatory. Suleiman al-Jamal said, "It is Mustahabb that he takes a pillar/wall as a Sutrah… Even if he wasn`t praying to a Sutrah or somebody passed in front of him, his prayer is valid. "{Hashiyat Al-Jamal, 1/436}.In addition, Al-Imrani said, "Even if someone passes in front of him, his prayer isn`t invalidated."{Al-Bayan, 2/158}.
The Fuqaha(Jurists) also stated that making too many unnecessary movements renders prayer invalid. "Refraining from unnecessary movements during prayer keeps it valid. If he made three consecutive actions: three steps, three unnecessary scratches or a big leap, his prayer is invalidated; whether he did so forgetfully or on purpose. However, little action or slight movements, such as moving the fingers doesn`t invalidate his prayer."{Al-Mokhadima Al-Hadrameyah, P.79}.
Walking towards a Sutrah, during prayer,outweighs someone`s passing in front of him as far as the validity of his prayer is concerned. This is because the former is likely to invalidate his prayer while the latter isn`t. Al-Imam An-Nawawi reported that it is agreed amongst jurists that a praying person shouldn`t walk to prevent someone from passing between him and his Sutrah, because doing so is likely to invalidate his prayer. By analogy, preventing the praying person from walking towards a Sutrah should take precedence. Kindly refer to {Shareh An-Nawawi`AlaSahih Muslim, 4/223}.
In conclusion, if the Imam makes Tasleem, then the person joining the prayer late shouldn`t walk to a Sutrah according to what an-Nawawi reported above. This is particularly since some jurists said that the Sutrah of the Imam is the Sutrah of those praying behind him, even after he makes Tasleem. Kindly refer to {Hashiyat Ibn Abdeen, 1/638}. And Allah knows best.