I know this is an old post but a lot of these replies are wrong. I play HD witch doctor for years and never had an issue dying.
1. You need your death passive always on spirit vessel
2. Get items that reduce damage % like Lakumbas bracers ukapien serpent kitty cat blood brother justice lantern etc.. unity is nice but if you can't find 2 right away use other options.
3. I'm using Jade harvester now on PTR with only 15 hours on my WD (with no rushing) I've completed level 57. You need soul harvest for the damage reduction so always make sure you have full 5 stacks. 10 stacks even better if you have Sacred Harvester weapon. Those bracers are godsend
4. Get a front line. I use the passive Fetish Syncophant but you also try something like belt of transcendence. I also use the belt that causes enemies to be slowed 80% affected by locusts swarm so nothing can surprise me or get past my front line.
5. Start slow until you have full stacks and a fetish army.. never take an unknown banner especially when you don't have your defences stacked.
6. Use appropriate skills and gems. Spirit walk probably best skill in the game to get you to safety. Horrify gives you 50% more armor so spam it in tough areas or use dogs to soak if you don't have fetish. Use topaz in your gear it helps with all res as well so you need armor and life on items more than all res. Legendary gems like estoic
I can edit and post more later but I have never lost a WD in hardcore. Neither should you. They are the best feeling for survival imo