Will the bean salad dressing that I made ahead of time still work?
It's fine. Vinaigrettes last pretty much indefinitely in the fridge.

If the oil was exposed to too much light or air it might have become a little rancid. Smelling and tasting it before using it on the salad is a good idea. I wouldn't expect anything like that after just a couple months.

Catija alluded to garlic above. Garlic in oil is dangerous because it has an elevated risk of developing botulism- however in a separated vinaigrette all the particulate matter is submerged in the vinegar portion. More than acidic enough to prevent any botulism.