it has been proposed here that Sakura might not be interested in getting her feathers/memory back due to the loss of Clonie, with the basis being declining the return of the last feather in Tokyo world. However this gesture is for me as of yet not a sign of the whole quest of Tsubasa now at an end or at least stopping-point. Even if the memories are painful, she would still want to get them back for they are not of Clonie alone (and for her they are not of Clonie anyway but of thin air she is speaking to) but also of his home, brother, father, Yukito and so forth.
If she refused now to collect any more feathers it would be a kind of running away and I doubt she would do it nor that CLAMP wants us to look at her like that (one running-away guy is enough
!)
It would be more probable to suppose that she left this feather since she is as kindhearted as she is and having heard C!Syao declare there are no more feathers in that world, she believes that Clonie will not then come back to take it.
After (hopefully) a little pause during which we get to know more of R!Syao and once the gang decided on the next course of action, I do see them travelling as before with the intent to get her memories back. I would not be too surprised if either she or someone would propose that the way to either get Clonie back or defeat FWR is for her to get the feathers but then somehow gain the advantage through the power she has.