It has been possible in the past, and the community which is developing the JB is well aware of the fact that many folks will have the tethered JB applied to their 5.0 devices. Heck, most of the dev will themselves.
So, if I were a betting man, I'd say we will be able to apply the untether over the top of the tethered JB. But nothing is guaranteed! It will probably be best to get rid of the semi-tether hack before you try and untether too, but that's just my personal speculation...