Okay, so Sigma is the bad guy who never dies for good. But the thing is, it is a virus that makes him bad. If his true form is now the virus, does that mean that the real Sigma is dead?
Perhaps in MMX he was the real Sigma gone Maverick, but he got destroyed. But the virus lived on, and took on his memories and personality to make it a more sentient entity.
So perhaps if they found a way to cure Mavericks, it would not bring Sigma back but rather just kill him?

