Face and Body Foundation that seperates has not gone bad - this will happen over time naturally. (You can sometimes even see it on bottles displayed on shelves at MAC stores, esp with colours that don't move very quickly) All you need to do is shake it up, and it will be fine. The only way you would know if it went bad is if the smell was off, anything rancid, funky, or unpleasant should go to recycling. (Face and Body normally has that nice grapefruit kinda smell)
The product has a two year shelf life from the time it is opened, regardless of when it was sold. (Look for the little symbol like a bottle opening with a number in it, it will tell you the number of months you should use it up within from the time of purchase, eg 24, 24 months or two years)
Having said that, putting it into smaller 1 or 2 oz bottles is a much easier way to keep F&B in your makeup bag or for travel, and the fridge is a good place for the remainder you are not using!