How long will probiotics last in fridge?

I have 3 bottles of Jarro-Dophilus probiotic capsules in the fridge. One has a use-by date of 2007, one 2006 and the other 2001. Yeah, I know. We didn’t realize we had 3 bottles, thought we just had one, and now I need to start taking it again and can’t bring myself to throw them away unless I know for sure they’re really dead. Do you know how expensive that stuff is?!
Any idea how long past the use-by date this type of probiotic will last in the fridge?