Well, for a start, while it's not really based in guerrilla tactics, the AI has no (or just extremely limited) threat selection at all. I have plinked at squads with a machinegun in plain site from some form of high ground (usually a building), and they are fully content to shoot at the ground dudes with garbage weapons who can't even get a clear shot on them. Adding some form of threat analysis would go a long way.
Secondly, as for dealing with long range attacks, Far Cry 2 provides some pretty good examples. If you snipe, the majority of troops will take cover and try to discern where the shots are coming from (meaning you must constantly relocate), and small squads will march out, usually under cover, searching. It leads to a system where, if you aren't careful, you will get caught even if you are constantly on the move and relocate after each shot. As of now, they just seem to do nothing and let you pick them off one by one.
Some form of communications could quite easily let them deal with or at least mitigate hit and run attacks. They could put in scouts and reconnaissance units to hide and track your movement, communicate to relevant squads, then set up ambushes along your paths. They could hunker down in a safe area and force you to attack them at a disadvantage. Practically all of of these, to some degree have been implemented in games before this, and there is little stopping the devs from coming up with their own tactics.