If you let it ferment all the way dry, then by adding your standard amount of priming sugar, you shouldn't have to pasteurize, much like a beer. Now regarding your exhausted yeast I would guess that the yeast will still be alive enough to carbonate. Did you add any yeast nutrients or energizers? The worst that could happen is you get an off taste or smell from stressed yeast. The least that could happen is it poops out a little early, and you have a sweet product. If it were mine, I would let it dry out, rack into a bottling bucket with a sprinkle of wine yeast in there, then bottle and pasteurize. Or you could add wine yeast now. How does it taste and smell now? What's your SG?