I agree with the part of with Watanuki taking over the shop, he'd have a purpose! :)
Well, Moro and Maru are there to guard the shop; without them, there is no shop so I'm assuming they'd still stay there with Watanuki. Perhaps something will happen to Yuuko? I dread to think that. I agree with a happy ending for her, rebwaters. Yuukos' too good for that, being honest. And she is tied to so many people and worlds, I'd doubt CLAMP would just end her life like that, really.