Do you think Nexon made a mistake with vindictus?

The idea is, no they did not. The game itself is a heavily modified and compressed version of the source engine. It DOES still use vtf's and vmf's and all that stuff (as my files in my sourcesdk folder and tf2 folder all say opened by vindictus launcher), but at a binary level. They edited the engine. Heavily. As apparent it is that it still is the source engine, this isn't a worry. Nexon can't halfass this because Nexon did not make it. DevCat is the producer of this game; in this case, Nexon is simply the publisher. They are using something good like Themida, I assume, and there's no legitimate threat like this in the future. At the most, it'll be more like a private server.

And, just to be a nit-pick, i'll say it again: NEXON DOES NOT MAKE THIS GAME. They publish it. As much as they all handle regional updates and stuff, it's still developed in the DevCat studio. What would be affected by the said scenario you posted would occur in the actual way DevCat produced the client.