When the dark matter sails through, is there still enough mass to keep it together, or do they evaporate? Are there "dark galaxies" to match the dark-matter-less ones?

I can't imagine how we'd ever find them. We'd have to get extremely lucky and find one that happened to lens another one behind it. That happens rarely enough with regular galaxies, and I imagine that those "dark galaxies" would be even rarer.

(And you'd still have to consider other explanations, like black holes.)

Personal theory: Possibly the Great Attractor has something to do with a very large collection of dark matter - potentially dark matter galaxies. Hard to say though until we figure out how to see that section of space.

As far as I get, dark matter is much more than normal one. However, we don't know what are the exact interactions between dm particles and hence cannot predict the shapes they will take.