So in my opinion this is probably one of the most survivable magic damage classes (barring priests that attempt dps).
I've only played the WL/CH as my third class to my WL/R, but I have to say that I bounce back and forth evenly between the two. Here's why:
1) Mind Rune. This skill alone is one of the key factors in my love for the combo. At level 50 (cap) it increases your HP by a massive 50%. The intell buff of 400 is minute and hardly noticeable but still nice. And to top it off it provides you with a 10 rage regen every 2 seconds. Meaning even when you're not in combat, your rage bar is full, giving you full access to all of your rage based skills without needing to build up power.
2) Psychic Extension. This skills makes your electrocution and energy influx strike from your champion side dark elemental magic damage skills. Additionally, it lowers their cooldowns to make them more usable. If you pay attention to those two skills you will notice that as long as the target has an electrocution state on them, Energy Influx strike ALWAYS crits. This leads me to the next point.
3) Saces's Fury. The next 5 crits you land gain 50% crit damage and can be used every 30 seconds. This stacks with the crit damage of your plussed rings, meaning end-game you're getting about 150% crit damage for 5 attacks, and lets not forget that if you use Energy Influx Strike while the target is electrocuted, it always crits. #pleasesircanihavesomemore
4) Rune Energy Devotion. This skill boosts your Dark element damage by 35%, and reduces your aggro generated by 40% at max. Can't beat additional damage and lower aggro generation... well except that you also gain 35 rage when you use the skill to keep your damage flowing, but that's hardly noticeable with Mind Rune active.
5) Saces's Impulse. The reason this skill fell at the bottom of the list (but still made it) is because it's only usable in Willpower Blade state, which is sometimes tough to enter. This skill heals yourself for 4% every second and boosts your intel by 45% for a whole minute. Do the math. That's 240% HP healed in one minute. Meaning you can almost die two and a half times, and still be regened back to life.
As far as damage output goes, this class is much different than it's WL/R cousin. The focus is shifted from the DoT powers and spamming Shadow Stab, towards sustainability and pumping out huge crits. Using the same gear as my WL/R (the void staff and elemental set) my WL/R deals 70k crits with puzzlement when the target is weakened. Using all the buffs from the WL/CH, my puzzlement crit for 126k. While that kind of damage isn't sustainable for a long period of time, it gives you an idea of the potential power that this class combo has.
So as an overview:
1) WL/CH has a super survivable build. 50% HP buff with a 4%/sec self heal is nothing to scoff at.
2) WL/CH seems to focus on the hard hitting high numbers at a slower rate rather than some of the other swift hitting DoT builds.
3) This build is still very party friendly. While the WL/CH sports 0 party buffs or enhancements, it allows other characters to do their jobs a little easier. Ex: Priest/healers rest easy knowing the WL/CH can take a lot of hits with their massive HP and self heals. Tanks don't have to worry about them pulling aggro due to their aggro reduction skill.
Overall, it's a super fun class. The challenge is choosing which warlock build is right for you.
PS. just CP'd my WL/CH: Ended up with 83k mattack, 160% crit damage (saces's fury buffed), and 106k HP (Mind Rune buffed)
I didn't get to figure in the HP buff from priest, but that just adds to it. Not to shabby for a magic user.