Basically their are other markets for them. Probably not as profitable. Who knows if they resell them for real cheap they may end back up on the BTC network.
BFL seems to only accept the FPGAs on upgrades, so this will effectively set a quite high price on the old miners. However, the ASICs does essentially the same thing, but so fast I wonder if the price/performance of the FPGAs will be so miserable in comparison, that they will be quite uninteresting, really.