Robbers come in groups of 3 to 6. I usually manage to get away (I never walk up to an "adventurer" on the overland map, but rather zoom in and walk towards the location, so I usually see them as the appear in the distance, and can zoom out and leave).
I haven't had any problem with shooting them first (which I do on robber quests once I have located them and gathered a posse [nobody but my character may use a missile weapon]). You may be able to run, but they're fast runners. Once they've got you, the best thing is to yield, in which case they steal your good stuff, but won't hurt you or your dog (and I think it may be possible to cheat by dropping your good stuff on the ground and pick it up after they've told you to run). If you fight (and don't have backup) they typically manage to beat you into unconsciousness (and sometimes death), steal your good stuff, kill your dog (unless it somehow managed to flee) and dump you half dead somewhere.
It's possible to kill robbers with hit and run tactics, but it's extremely hard without a fast character (and very hard with one).
If you run into them in hyperspace and are yanked out of hyper warp yes, they'll be right on top of you as you're zoomed in.