Responses
Yeah they didn't talk much about it. I personally think that back when Clow was alive, Yue never transformed into Yukito. Clow did know of Yukito though since he has a premonition that Sakura and Yukito would end up together (which didn't end up being true due to Touya and Syaoran). I think there will always be a use for Yukito because Sakura will eventually die just like Clow and Yue will need to slumber. Yukito will exist while they wait for a new master. If Yukito doesn't exist anymore, then Yue will likely die from running out of power (Yue can't eat while Yukito can to try to sustain them both).
When Yukito is just the form Yue goes into, to save energy/stay hidden, what will happen to Yukito, once everything is over? I know, that the anime never really touched on that, but I guess Yue doesn't want to stay asleep inside Yukito the whole time, it must be just as boring as for Kero - who was stuck in the book for years.
I mean, it's comfirmed, that Toya and Yukito are a pair, that would be pretty sad, if Yukito as some point wasn't coming back, yo know what I mean?? Did they say something about that further in the Manga? If I remember correctly, Yue remembers everything happening to Yukito - so no sexy time for Toya and Yukito lmao.