Given a game where:Source code is licensed under a free (libre) open source license, e.g. GPL, MIT, etc.Assets such as images and music are licensed under Creative Commons Non-Commercial.Is it correct that making the assets available non-commercially only prevents other parties from distributing the whole package (i.e. executable w/ assets) for a price, but those other parties could still undercut the creators' attempts to sell it traditionally (e.g. distributing it for a price) by distributing it for free, since they could legally obtain everything needed to rebuild the game?Would dropping just the assets' CC license and instead retaining full rights for them under Copyright make it illegal for other parties to distribute the full package?  This would be assuming no one had obtained a copy of the assets while they were under the CC license.This question was inspired by the required proprietary parts section of this Wikipedia article on OSS business models.  It describes this exact scenario for the Steel Storm game, however for the reasons above I wouldn't expect this example to actually be viable.
Is OSS with CC-NC-licensed assets effectively impossible for the creator to sell traditionally?
creative commons;monetization
Is it correct that making the assets available non-commercially only prevents other parties from distributing the whole package (i.e. executable w/ assets) for a price, but those other parties could still undercut the creators' attempts to sell it traditionally (e.g. distributing it for a price) by distributing it for free, since they could legally obtain everything needed to rebuild the game?Yes, contents distributed under CC-NC can be re-distributed for free. Since the binaries are distributable under a libre license, the complete package can be re-distributed for free, so other parties could undercut the original developer by giving the game away.Note that if the CC license doesn't allow adaptations to be re-distributed, then any identifying elements in the assets can't be removed by the other parties; that may make it less interesting to undercut the original author in this way (at least for the other parties; recipients only looking to get the work for free presumably won't mind).Would dropping just the assets' CC license and instead retaining full rights for them under Copyright make it illegal for other parties to distribute the full package? This would be assuming no one had obtained a copy of the assets while they were under the CC license.That's a big if! If anyone obtained the assets under CC, then the previous situation still applies, since CC licenses are irrevocable; as long as a recipient doesn't lose the license by violating its terms, the game can be distributed for free. (I'm guessing you know this since you stipulated the assumption.)If no one has the assets under a CC license, no one but the copyright owner can distribute them, and we end up in a similar situation to many of id Software's games: the engines are free, but no one can re-distribute the full games without an appropriate (commercial) license from id (or Bethesda nowadays).As to your main question, I'd argue that this type of scenario doesn't make the assets impossible to sell, merely difficult. There can be value in other aspects of distribution, e.g. presence on Steam for a game, or a physical package...