Could Yue/Baiyue people have maintained themselves in southern China (it doesn't have to be all of it), either on the form of one state or several, or as a constituent people of one big chinese state (as Hui)?
Entirely possible. Considering that the China Plains' interest in the Baiyue (at least, in the farthest south) was almost entirely initiated by the uniquely megalomaniacal character of Qin Shihuang, and then again by the equally controlling character of Han Wudi (who exterminated Nanyue State), it's not necessarily the case that the Baiyue has to fall.
Of course, as people have mentioned that the Northern China Plain is always going to be more agriculturally rich/politically united than the hills/valleys of the Southern Hills, so there is incentive for any Northern regime to move south. But that's a) highly dependent on the stability of said northern regime, and b) dependent on whether said northern regime has more pressing things to deal with, i.e. the Mongols.
Under extreme pressure, the northern regimes will retreat from parts of Southern China. Hainan Island was constantly being abandoned and of course you have the numerous Shanyue quasi-kingdoms in the mountains of Fujian well into the Eastern Jin period in the 4th century AD.
So for a Baiyue southern China, you'd need pretty permanent fragmentation in northern China, or extreme pressure from the Mongols or some other northern people.
Baiyue Southern China will be pretty fragmented, with the numerous mountains and hills making communications difficult and local defense easy. I foresee major power centers to emerge in the Pearl and Red River valleys, maybe the Xiang and Gan Rivers too if northern Chinese regimes lose their grip on those regions.
As far as we know the Baiyue were a pretty water-savvy people (not surprising considering riverine/coastal movement was pretty much the only effective way of communication there), so if sufficiently advanced I suppose they could develop a good maritime culture. I still think Sinicization is quite likely considering that many of the northern Baiyue states are going to have to pay tribute to a northern Chinese regime, which allows for cultural and technological diffusion.