Reformed might've been a bit strong of a word. I do not know much of the madness of Isaac Clarke, but one madness is not like the other. Vaas is more insane than mad, if one can split the words. An insanity that he controls, that is the basic way that he lives his life by. He is unpredictable and can lose control of himself, yet he is able to regain control just as quick. I guess my view of Vaas is that he is more of a functioning madman (e.g. the Joker, only less refined).
As for the reform, I can see how it appear difficult for a man such as Vaas to turn from evil, but I think it entirely possible. In Far Cry, Vaas, even if he was following Hoyt, seemed like his own man. To me, he was the main antagonist and despite being a villain, I could still see him as a "good guy". It seemed to me that everything around Vaas is merely there for him to play with. An idea that sprung to mind would be a situation or organization similar to the "Suicide Squad" agenda.
If there is too much doubt regarding Vaas, however, I will change my mind :)
