Rubio was likely telling the truth. He wasn't interested. On that day.
Time and perspective are powerful things, and the appeal of ascending to the 2nd highest office in the nation should not be underestimated. He's a smart guy, and knows that being on that ticket is a win-win. If Trump wins, he's VP and heir to the throne. If Trump loses, he can go forward with good will from the Trump wing AND still hold his support from establishment and moderate voters. The only question is if he's able to swallow his hurt feelings and move forward for the good of himself AND the country. I think he is.