Here’s my take:
Yes, Lin is very popular right now. He’s ‘hot’, some might say. But I think the driving force behind Hamilton is truly the popularity of the show itself – though I would never discount the theory of Lin being a major reason some people are going to see it.
The music is grabbing people, which is also a huge factor. It’s appealing to masses of young people, who then take to twitter and spread the word, and so on and so on.
When I saw it back in January, I sat next to a girl who didn’t know the music, didn’t know any of the actors, and didn’t know Lin, similar to what you mentioned in your original post. What she knew was the popularity, the rumblings of splendor about the show, and that’s why she got a ticket (or, more accurately, why she asked for tickets for her birthday, as she informed me).
Hamilton will continue to dominate after Lin & co. depart, and for well after that.