I wouldn't say it's mandatory but a lot of times it can add a lot more depth to a story(if it's done right, there should be a logical system to it, and limits to what you can do with the magic.) but it really just depends on the story you are telling.
Yeah I don't think you have to phase him out per say, maybe the main character meets your immigrant and the immigrant follows him on his journey? Or throw a curve ball and have what people think is the main character meet the immigrant, but later on in the story kill your 'main character' and...
Hmmm idk I just feel like magic can be too generic a term, and magic means something unexplainable(inherently, most books tend to explain it thoroughly, which makes calling it magic redundant) electronics would be magic to a person from 2,000 years ago, but to us it's perfectly normal and...
Like in the night angel trilogy by Brent weeks, it's called talent. In Mistborn it is allomancy. I'm building a world right now and I don't want the magic to simply be called magic, and I was wondering what some of you may have called your magic?