I'm more optimistic. Dominion isn't particularly resource-intensive (i.e. doesn't require a lot of hardware), and doesn't evolve over time (i.e. doesn't require a lot of maintenance). In addition to iso, at least three different forum members have developed free simulators that run fast enough to serve as the back-end for all of Goko.
Alternatively, there are plenty of game servers, even for server-driven multiplayer games and low-latency real time multiplayer games that cover both maintenance and development with just ad revenue. Any such company could pick Goko's Dominion or reimplement it better with ease. The only real danger is that Goko/RGG somehow screws up the transition.
I made my own card game a while back and looked into what sort of legal protections there are.
Quite frankly, its incredibly difficult to trademark, patent or even copyright a card game, and even more so an online computer version of said game, as long as the copiers don't use the official artwork, or quote the official rules. (In fact, that's pretty much the only way to defend a card game). Most games avoid these issues because it's not that easy to make a card game, its not that easy to make an online game, the threat of a lawsuit (even if it would go nowhere) isn't really worth the trouble for most people, and game publishers rush to establish market presence so everyone knows who the ripoffs are.
Pretty much the only reason nobody has made a competing site for Goko is that everyone with the ability and inclination to do so likes Donald X. and/or RGG too much to do that.