With the way soul shards generate now, you can keep a non-demonology-spec voidwalker alive effectively forever on most elites. Magic-casting elites are a bit tougher but it's not that bad. I solo'd Sarathstra at 74(or was it 76?) on my solo affliction-spec lock while leveling, and was never in any danger of either dying or running out of mana. Just put a couple points into improved health funnel and the voidwalker taunt/aggro one and you'll be set.