No, they don't die. If they go to 0 health, they disappear from the battle and reappear sometime later (even if the same fight is still going on).
It was easiest to test this with the skeleton king. My templar "died" a couple of times and came back 30 seconds or something like that later (Although that number is just an estimate, I haven't measured).
Stage 1
Kill all the worms which is trivial.
Stage 2
Focus on Belial and let your companions handle the little guys for the most part. Make sure at the end of this round you are full on spirit or else you'll be in much worse shape.
Stage 3
From what I can tell, Belial has 3 main abilities:
- Whack you
- Spit green stuff in sweeping motion
- Green exploding void zones
It requires a little concentration, but if you counter each one individually, it's much easier.
When he whacks you, you are in his melee range and it doesn't hit very hard, so you can basically ignore it.
When he spews green stuff, make sure you 300 life and you should live through it.
The green exploding void zones are the hard part. These will tag you for bleeding damage while you are standing in them and then they pop you for 500-600 when they explode. The only real strategy for these is to run away from them. I have found that running around the outer edge of his zone gives you the most room to work with and tends to be a lot less busy so you can see yourself the whole time.
This is not a DPS fight! Focus on keeping yourself at full life. I used the aura that heals you when you use spirit and the one that gives you 100 extra spirit. I don't think the mantras I had at this point are particularly useful for this fight, but I used the one that increases dodge to help with the first 2 stages. I also used the aura companion spell and the heal party spell. I had the enchantress follower with me.
The basic strategy is to keep your spirit capped off, and as soon as you take damage, blow some spirit. During the slow parts, run up to him and build your spirit back up. Don't forget to use your potion if you get into trouble and don't worry about your companions, they will figure it out. The last piece of advice is to not go crazy and blow all your heals when you take damage. If he hits you with a whack as you are lighting up your spirit orb or you take a green spit, just cast a single damage spell that uses spirit and save the big cool downs for when you are running away from the green voids.
Lastly, health globes do pop up in melee range quite often. It's more important to keep yourself topped off than it is to DPS.
Best Answer
If you start the mission "Trailing the Coven" and leave New Tristram heading towards Old Tristram, you can find Rumford's corpse on a bridge not far from the town gates.
Clicking on him will make your character deliver a short eulogy (in my Witch Doctor's case, he said "Rest easy, friend..."). There's no in-game dialog that explains exactly how he died, but given the events of the mission prior, it's likely he was slain: