As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.
There were some words that could be used to describe this situation, such as:
1. Multi-changing: This person's multi-changing makes him/her no longer the original self.
2. Self-Subversion: This person has experienced a huge change that has completely changed him/her and is no longer the original self.
3. Unrecognizable: This person's change makes it impossible to recognize his/her original appearance.
Change everything: This person's change has made him/her a completely different person and changed everything.
5. Change of ownership: This person's status, identity, personality, and everything else have undergone earth-shaking changes. He/she is no longer the original.