I bumped into a robber ambush once with a Companion and 3 dogs in my group. In the end, the dogs killed 3 of the robbers' total, I killed two, and my Companion got one. The dogs didn't have a scratch, the Companion died.
The dogs actually worked as a pack, taking on one at a time. The robbers came as a group of three followed by the others, staggered.
Imo, dog packs are viable against robbers and Njerp, although the latter may have their own dogs now and those really can mess up the contest because they'll flee and then return to fight again.
I've had single wolves and a solitary lynx rip my pack up, otoh. I wouldn't willingly commit them to combat with those types, especially against a wolf pack. In fact, there was a time when a single bull wounded all three dogs when I let them run him down. Contrary to that, my packs have done pretty well against bears as I've never lost a dog when they fought them.
And, yes, you CAN lose a dog when they get too far away. If you get up north, those tribes often have hunting horns for trade, useful for recalling your dogs.
The dogs heal some really nasty wounds. If they're hurt badly, they will constantly try to flee, so, keep them tied up when they're in that condition until they heal enough to lose the 'fleeing' trait.
Edit: Severely injured dogs will attempt to "escape", not 'flee'. While in that mode they won't eat when you feed them, despite their 'starving' aspect.