Yes, Clinton will win without the support of Millennials because she has so many more people who want her to be president. She has the support of women and minorities in ways that Trump will not be able to overcome. She has proven she is the sane choice during this election.
It doesn't matter if the little people support Clinton or not. She has the support of the political elite. That is all that matters. They will do whatever it takes to make sure she wins. There are a lot of baby boomers that don't trust Trump. They will carry the election for Clinton.
Hillary's "social media game" is not good, and may even be worse than Trump's. Her "Delete your account" tweet made many young people, myself included, cringe with secondhand embarrassment. A tweet like that is an obvious attempt to use humor that is popular with the Buzzfeed and Jimmy Fallon crowd, who are likely what many see as stereotypical millennials and young people.
The only way she will be able to win without the support of so-called "millennials' is if they do not come out to vote, like they did when Obama was elected. The good news is that the majority do not seem to be supporting Trump either, so she should not be as concerned.