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.
In most cases, you can. However, you need to check if the name is available and not protected by intellectual property rights. Also, consider the potential legal implications if the name is too similar to an established brand or entity.
Well, Megumi's story in the manga was full of twists and turns. She had to overcome various obstacles, and there were also some unexpected developments in her relationships with other characters.
Nope, Megumi is alive. The author has chosen to keep Megumi's character alive to continue developing their story and interactions within the manga's world.