If the electoral college has the final vote, could all the state votes be overturned ?

YES, AND ANYONE WHO SAYS OTHERWISE IS MISINFORMED OR LYING

Look.... what's possible, and what's likely is a fun game to play...............

if this , that and the other thing happens, and pigs fly past a blue moon on the 5th of January, then maybe it's POSSIBLE.............blah blah blah-.

In short..........NOT Happening. Joe Biden is the President Elect.

He WILL be sworn in on Jan. 20th.

all of Trumps ranting and pipe dreams put together, and blessed by RUSH, and Moscow Mitch, will NOT change the outcome at this point.

Joe Biden is the New President. Period.

There is theory and then there is practice.  

On the theory side, the U.S. Supreme Court has upheld laws by states requiring electors to pledge to support their party's candidates, requiring electors to abide by those pledges, and creating provisions to enforce those pledges.  States fall into five categories when it comes to electoral votes.  

States in category one either do not require electors to sign a pledge or do not require electors to abide by those pledges.  There are seventeen states in this category including Texas, New York, Pennsylvania, Illinois, and Georgia.

States in category two mandate that electors vote as pledged but do not have any enforcement provision in state law.  If an election ever came down to a faithless elector in these states, we would probably see some type of litigation over how to enforce the pledge.  There are fifteen states in this category including Florida, Ohio, Virginia, Massachusetts, Maryland, and Wisconsin.  D.C. also falls into this category.

States in category three mandate that electors vote as pledged and enforce that pledge with a fine only.  Three states fall into this category including California.

States in category four mandate that electors vote as pledged and either cancel the improper vote (replacing it with the proper vote) or replace the elector that attempts to violate the pledge.  Twelve states fall into this category including Michigan, Washington, Arizona, and Minnesota.

Finally, the two states in category five enforce the pledge by removing the elector attempting to cast an invalid vote and fining that elector.

So, in theory, only fourteen states cancel the improper vote, and the most that an elector faces for violating their pledge in the other thirty-seven jurisdictions is a fine and the loss of their reputation.

In practice, the electors in each state are the slate that ran with the winning candidate.  These electors are chosen by their state party and tend to have a long history of working at various levels of the state party.  In short, these are not the type of people who will go against their party in any significant level.  Putting aside the situation in which electors were pledged to vote for candidates who died after the election, we have rarely had more than one faithless elector in a given election.  (Of course, 2016 was an unusual election in which we had seven "successful" faithless electors and three more attempted faithless electors.)   And for the most part, faithless electors have tended to be from the losing party with the "faithless" vote being mostly a protest vote.

No. Trump is a loser...

On paper, that is possible.  Each state has its own particular laws about elector selection though, and there is a federal law that requires states to have that mechanism in place on election day (can't change the law on selection after election day), and many states do not have any legal way for electors to vote other than the way the state voted, so as a practical thing, it is extraordinarily difficult and cannot happen at all in many states.  But it is possible, at least in some states.  Not true for all, though, so the answer to the question is no.

Edit: Check this out. I found a document from the Texas 2016 race, and the electors were mainly for Trump, but Hillary isn't the only other name they could vote for.

"FOR PRESIDENT: DONALD J. TRUMP received 36 votes, RON PAUL received 1 vote, JOHN

KASICH received 1 vote and no votes were cast for any other person for President of the United States. 

No elector voted for Hillary in Texas. But Ron Paul and Kasich were voted for.

https://www.archives.gov/files/electoral-college/2...

They aren't overturned, as I understand it. They call them "unfaithful electors" and some states have laws against that. Hillary, when she lost in 2016, wanted electors to be unfaithful. The thing is, the electors involved knew what she was up to, and voted for Trump anyway. One didn't. if I remember, but I would have to look it up to find out what the reasoning was. There was at least one elector who was insulted that Hillary had one elector change the vote to her, so he changed to Trump just to show this was an honorable thing to do.

The Supreme Court ruled in July that electors have to vote in line with how the voters in their state voted.