Pheace: He can't however tell Valve to not give the mod to the people Chesko already sold the mod to through Valve.
Phasmid: Yes, he can, if it uses his copyrighted material he can do
exactly that every bit as much as Sony/ Universal/ BMI/ whoever could if a Rihanna song had been added as a soundtrack. Valve has, and is continuing to infringe his copyright by offering it for download, even to (actually, it is worse because it is to) people who have paid for it already. The only reason they're doing so is because they don't want to refund purchasers, they can do it technically and they have an absolute obligation to do so legally- every bit as much as I would if I put Skyrim up for download for $5 without seeking the approval of its copyright holder.
That is
exactly the same thing Kim Dotcom/ Megaupload is accused of doing, profiting off copyrighted materials. It's worse than plain piracy because they are making money off of it and refusing a proper response. Of course, as a multi billion dollar company they can probably get away with it due to lawyers and lobbyists if necessary- and because they're pirating off people who do it for nothing and don't have a MPAA/ RIAA equivalent- but it is copyright infringement and if told to remove it they have an absolute, absolute, obligation to do so.
What are you even talking about. If anything Chesko isn't the one to have anything infringed on here. He opted to sell his mod through Steam. He can't then, after doing so, get iffy and try to pull it back from the people he already sold it to. And this is talking about the part of it that was clearly created by him, the part he was arguing he's supposed to have the right to do anything with, including withdrawing it. Perhaps he should've bothered to read the Eula before he entered into this deal? Same thing as he probably shouldn't have started selling a mod that wasn't entirely his creation without contacting a lawyer which they even recommended him to do?
Now Fore, he may have an argument for getting Valve to pull the content if he issues a DMCA, but he hasn't as far as we know. In fact, Chesko choose to pull the mod himself after discussing it with Fore. So as far as Valve knows, the modder is just pulling out and is trying to pull out more than he agreed to (knowingly or unknowingly).
Here's what he should've read before he sold his mod
You may, in your sole discretion, choose to remove a Workshop Contribution from the applicable Workshop pages. If you do so, Valve will no longer have the right to use, distribute, transmit, communicate, publicly display or publicly perform the Workshop Contribution, except that (a) Valve may continue to exercise these rights for any Workshop Contribution that is accepted for distribution in-game or distributed in a manner that allows it to be used in-game, and (b) your removal will not affect the rights of any Subscriber who has already obtained access to a copy of the Workshop Contribution.