The president isn't elected on election day.
The president isn't actually elected until the members of the electoral college vote and their votes are counted.
But no one ever suggests that the person who won the states with a majority of the electoral votes isn't president until the formality of casting and counting electoral votes are counted.
But wait, you say. Electors are required to vote for the candidate that won their state and thus you can't compare that to the nominating process where superdelegates can vote for whomever they want.
Actually, in at least 20 states, there is no law compelling electors to vote for the candidate that won the popular vote in their state. And only two states invalidate the votes cast by "rogue" (or "faithless" electors. The rest simply have provisions in their laws for punishing a rogue elector after the fact, but their votes stand.
What this means, is that in 2012, if the electors in New York, PA, and Illinois -- all states with no rogue elector law -- had wanted to switch from Obama to Romney they could have, and the election would have been thrown to Romney.
But wait, you say, that's ridiculously implausible even if theoretically possible. And you're right. And the reason you're right is that the electors generally are party regulars who can be expected not to go rogue. Just as the superdelegates generally are party regulars. And they too can be expected not to suddenly change horses.
In all likelihood, if and when Clinton obtains a majority of pledged delegates (and at the moment that seems much more a question of when than if), she will follow the lead set in 2008 by Obama and roll out a new group of previously uncommitted superdelegates who will cite to her having obtained a majority of the pledged delegates as the reason they are now coming out in support of her nomination. And those additions, together with the absence of any sign of defections to Sanders, the contest will be, for all practical purposes, over. And Clinton will, appropriately, be recognized as the party's nominee.