The other idea from the class that may be naturally hunting them (Rogues) is they can hold backstab until the casting of that heal starts. The rogue would then get behind and backstab, although I also add in Intimidation and pickpocketing (that's just for fun, and usually for combat initiation). The backstab has a chance to interrupt casting, plus neutralize the heal. Initimidation has a chance of giving fear also.
Just tried killing one off and realized what it was doing, but I couldn't do it successfully (I need practice in driving...).
FYI, they may also cast Dispel Magic. My SoW went down also in that fight after what may have been a spellcasting.