Bluesand - chances out of 10 that they'll reproduce? I'd say 11 or 12. As to whether any fry will survive, that depends on how much plant cover is in your tank. Livebearers are notoriously bad parents, it's not unknown for a female to drop a fry, turn straight round and eat it. They produce around 30 fry every 4-6 weeks, in the hope that some will survive to maturity. In the wild, the fry would swim as quickly as they could to the shallows where the adults couldn't follow. In the aquarium, they don't have that opportunity, so some java moss acts in much the same way. May I suggest, if you have room in the tank, to get another female or two, as this will divide the male's, ahem, "attentions" between the females, and allow each of them something of a rest. In extreme circumstances, a female platy can be stressed to death due to the constant "attentions" of a male.
Phantomlink, some of my comments also apply to your situation. I find it impossible to believe that none out of 8 females have ever been pregnant. I find it plausible that they've been pregnant, and that all the fry have been eaten, especially if the stocking level in your signature is accurate.
I kept platies for some while, and never once saw a fry, although I was aware of the females displaying "imminent drop" behaviour.