Actually you can change the flint on a Bic, it's just tricky to reassemble and probably not worth the effort.
If you do have any Bics with leftover fuel (and you're a total pyromaniac), you can use them for fire starters, just crack one open over the fire pit and you'll have a lot of fire very quickly.
Not that I've ever had a flint wear out before the butane is gone. I like to collect Bic flints to use in other lighters.