I've had tatsoi, bok choy, mustard, komatsuna,and maybe others from a 'spicy salad greens' mix. I think in general they can take some frost but probably not live all winter. I now get odd volunteers but no idea where they are on the spectrum of brassica greens, or even wild. I never ate mustard greens in the past, but grew them along a south facing wall and here, they were productive all winter that year. And tasted good, up until spring near flowering got them hotter. In an open garden, I think hard freeze eventually gets them. Then again, I did have flowering mustard this spring, and more seedlings this summer. So it seems like some lived thru winter here zone 7.
Kale will look awful in winter but I think will live and give you spring greens before flowering.