I think the particular strength of being a nightblade with destruction and restoration staff is that you can switch between damage dealer and healer at will. You can't spam your way to victory with breath of life like a templar can but what you can do is constantly pump out heals over time to everyone around you. I've got a VR1 nightblade healer and I can't remember if I've been main healer in a veteran dungeon successfully but I've definitely done it in many non-veteran silver key runs, and it's also a killer soloing build. The key to it is that speccing for healer overlaps a lot with speccing for ranged magicka dps so even though i've got the eyes of mara robes, ritual birthsign etc. I can still do serious damage with siphoning and destruction staff skills, and the siphoning skills heal me and my teammates. So if they're not taking much damage I can actually act as a healer without even casting heal spells, just DPSing away at things with funnel health. As I say though, I don't know how well it stands up to the cruel reckoning of veteran dungeons