@sun You will certainly make the same or more money as you would have by making the whole game proprietary if you make the art proprietary and make the software free, but that would certainly miss out my my purchase as I don't pay for proprietary art, or use proprietary payment methods for software.

If you eventually release the game and art etc under a free software license, that is a lot better than most attackers, but that wouldn't make up much for the wrong you previously did.