I'm not saying Rubio is on top or anything. So please don't take this as any sort of a prediction. Rather it's just a speculative observation. Rubio may have finished third tonight but he's a lot better off now than he had been. He has a chance now to unite establishment Republicans now that Trump is demonstrably no longer omnipotent and people like Chris Christie (1.8%) and Jeb! (2.8%) begin to prove themselves not viable.
Again I don't think he's the favorite for the nomination yet but he is intriguing for this reason. If Rubio is the nominee, he is an establishment favorite, yes, but he still will benefit from the continued rabid support of the conservative base Trump and Cruz are currently invigorating. Trump/Cruz voters are mobilized because they "want to take their country back" from perceived enemies among non-white, anti-Christian, and foreign threats. Regardless of who the GOP nominee is, the perceived enemy will still be the Dem candidate for them. This is even more pronounced if the nominee is Hillary Clinton who has (justifiably or not) been a major focal point of right wing hatred for decades. Rubio might not be their favorite son. But he's less boring than Jeb! and they will definitely turn out to stick it to Hillary.
Contrast this with the Democratic side where it doesn't really work that way. Bernie's voters are mobilized specifically because they want to overturn the crushing influence of the money power. If Hillary is the nominee they will have already seen the campaign as a failure. Many of them will still vote Hillary but they won't turn up in great numbers or with much passion.
So in a Rubio vs Hillary race you're going to end up with an enthusiasm gap which will greatly advantage Rubio. This would also be the case in a Trump/Cruz vs Hillary scenario but the advantage of Rubio is that fewer people will show up just to vote against him.
Anyway so there's your path to President Rubio. Not saying that's a lock. Just that it's a thing you can map out now.