Presumably this is just going to some sort of one-off gig or mini tour.
But long-term, I agree they'd be better off just plugging on with Heaven & Hell. Find a new singer - not a big name with another full-time gig to juggle - and make it a proper, permanent band.
Even if there was a Sabbath reunion, Bill would soon bail out and Ozzy would be disappearing periodically to do his solo stuff, leaving Tony and Geezer to twiddle their thumbs. And let's not forget Sharon sticking her bloody nose in and stirring things up...