This is still in a weird rhetorical state now, since I guess we don't know what Valve's going to do, but I still think it's better to not pay/submit a ticket in this instance.
If Valve doesn't revoke the game: The dev gets paid, he gets a free game, Gaben picks up a minuscule tab for the mistake.
If Valve does revoke the game: He buys it like normal, dev gets paid, Gaben gets even more cupcakes.
If submitting the ticket were the difference between those two, I'd definitely say to not submit the ticket. Part of it comes down to the same debate that comes up with piracy and copyright, of whether getting free versions of something freely and infinitely replaceable is acceptable. I would personally say that the only thing that's relevant when paying for virtual goods is that the creator gets paid for it. It's not so much a stealing from the rich mentality, as just not respecting the middlemaning of virtual goods as something positive for either the consumer or the producer. Valve taking a cut is normally the same necessary evil we deal with for all other stuff not bought directly, so if you can get out of it (especially on the internet, where so many of the mark up reasons aren't relevant), there's no reason not to.
I'd rather not derail this with a discussion on consumerism, copyright, and capitalism, but I think we can all agree that he was under no obligation to submit the ticket, so either choice is acceptable.