As combat stands right now, any NPC you hit who's weapon has enough range to hit you, will return fire after they're hit, regardless of whether or not they have a sensor reading on your square.
Is there any chance this will be changed in the future?
Also, will the same hold true in PvP? Meaning, if I'm holding a 9-range weapon, but my sensor only covers 7 squares, will I auto-return fire if attacked?
No, we're not going to let you stand outside range and be beyond recourse. If you initiate Combat, your opponent is going to be able to attack back, as long as their weapons have the range to hit you.
The difference will be, when their aggression is enabled, they'll have to move into range before they will attack you independently.
A bit of a shame for any tricksy hobbit using a Xerrol Nightstinger. I mean, the whole point of that thing is to remain hidden from return fire, regardless of the range the weapon was shot from.
I would also expect if for some reason they could see you (imagine if bandits could use other bandits' sensors!), they would continue to move toward you until you were out of their perception range.