In Tsubasa: Reservoir Chronicle, Princess Sakura (also referred to as Princess Tsubasa) is cloned and replaced. What happens to Princess Sakura and what happens immediately after the switch for both Princess Sakura and her clone?
The original Sakura was taken as prisoner by Fei Wang.
He took the original Sakura and made the clone to avoid the risk of having Sakura dead during the journey of retrieving her feathers, to have the upper hand that if ever the clone fails (dies during the journey), he'll still have the original and can create another clone.
The clone was the Sakura who journey with Syaoran and the others. At their journey at Tokyo, where the real Syaoran showed up and thus revealed that the Syaoran with them was a clone, Sakura gained another feather that made her aware of her real existence as a clone. That was why Sakura was acting coldly towards the original Syaoran (knowing she was just a clone). Later on, Syaoran Clone (who has no heart now and was just following orders to get all Sakura's feather) learned that the original Syaoran has a feather with him and thus the two Syaorans started a fight. And because of that fight, the Clone accidentally stabbed through Sakura as she tried to protect the original Syaoran from being stabbed, making the Clone shocked as well. Then before perishing, she told Syaoran that she was just a clone and that her Sakura was not her. Apparently, the clone Sakura loves the clone Syaoran. And then she perished into a cherry blossom.
As far as I know, along with clone Syaoran, the clone Sakura were resurrected by Yuko because she was feeling guilty because she was the sole reason for why everything happened.
P.S., I edited my answer to answer your edited question. Contains a lot of spoiler but don't blame me, your question's scope wasn't that narrow so I answered in general. Hope this helped.