As a necromancer I find that there are 2 great ways to deal with me in this state. Like you said the first is to run away and LoS. Since I lack a speed boost that is the best way, but remember that I can Dark Path you if you stay in LoS.
The other option with works out rather well is to chain stuns, dazes, or interrupting abilities like a knockback. Many Necro's will sit on the auto-attack of Life Blast but since it has a cast time you can interrupt it. However, it depends on their build since they could pick up stability making this option moot.
A small side note.
This is also true if they enter DS shortly after exiting it because it takes a bit of time to build up a lot of life force.Be careful of this. Unless you SEE their Life Force when they exit you shouldn't assume it will be almost empty. Many will drop in and out of DS to keep maximum uptime of near max LF. Also, there are a couple of abilities in the right situation that can let a Necro recharge nearly half of their LF in a couple of seconds so be aware!
Proximo Admin replied
705 weeks ago