Is it possible for Clinton to win the November Presidential election without being on Democratic ticket?

Hillary Clinton just said that, "this is far from over." and earlier talked about going into overtime...That makes me wonder if her plan is to keep campaigning and gathering votes up and then run as an independent for the November election. Would that be possible? It makes no sense for her to stay in the race if she won't have enough delegates, especially when she says "this is far from over," and the head of Democratic party has made it clear there is a deadline to have the Democratic nominee.