Dan suggests you inspect the debris and tracks around the cave, first. Perhaps that will give you a better idea of whether the raiders are here or have already gone.
Aelric thinks you should wait and watch a while. You're in no rush to attack - maybe you can learn something by observing.
Martelo is concerned about the risk of waiting and having more raiders arrive. He wants to go ahead and check out the cave. It looks like the raiders are already gone. If they are still here, they won't be expecting a frontal assault!
Mistress Faye suggests that she scope around and see what her nature sense tells her. Sometimes the plants and animals in an area can tell a lot about a situation...
Another possibility comes to mind: that you shout out to the raiders in the cave that they are surrounded and if they do not surrender, they will be killed.
Another possibility comes to mind: create a distraction outside the cave to see whether it draws anyone out of the cave. It could facilitate things if you don't have to fight the raiders in the dark cave...
Some other creative option? (please comment)