Many ants can grow a new queen from their remaining egg supply as needed, so I should think killing the queen of an ant colony would be equivalent to killing a Darklord in his Domain of Dread; it might let you get out, but the horde will be stirred into frenzy and the root problem will regenerate in days or weeks.I think the biggest problem with Giant Ants is that there is only one real story to tell--you invade the nest and kill the queen, or plant a magic bomb or some other mcguffin to take out the hive.
You can't realistically take out an entire hive of ants yourself, (whether they come in hundreds or thousands) and they don't really have any potential for negotiation or mystery, for the most part. They aren't likely to work in concert with anything else.
Also, I believe that giant ants, again like Half-Life 2's antlions, are best used as an environmental hazard. When you're caught in a blizzard, your goal is not to hunt down and kill the winter wind--okay, maybe on occasion that is your goal, but not regularly speaking. You avoid too much trouble (ha ha ha), make your way through the sprawling underground colony (there can be some beautiful sights down there), maybe get lost and encounter something else in the depths of the hive, and get out through a different passage. Hopefully, nearer to where you want to be. Used in this way, they have the appealing side effect of helping to immerse your party in the world you're trying to create.
And, on a different note, the armies of sentient beings are usually also too large for five daring mercenaries to wipe out singlehandedly. Does that mean that wartime campaigns are doomed to repetitive boring futility? Oh, hell no! Most of the things you can do with an army as your nemesis could equally be done with, well, the chitinous monster of your choice. Ever heard of Starship Troopers?
Or suppose you need to retrieve a McGuffin from the ant colony? See again Half-Life 2's antlions, whose larval extract can be distilled into (basically) potions of ethereal projection--which, as it happens, allows certain trained individuals to heal wounds which would otherwise equal death.