Technically, he is not yet elected as President. That happens when the electors actually submit their votes. I think this happens in mid December.
If there is something there and it came out before then, I guess the electors would be free to vote for whomever they chose. They could vote for Biden or McCain or even Hillary I guess. Some states have rules for electors that make them vote the will of the state but if this were to come out....
Now if something like this happened it would lead to civil unrest and rioting on an unpresidented level. It would probably take the National Guard to break it up.
I think this all goes away but I believe if enough lawsuits are filed, maybe this could gain traction. I want to see a real birth certificate, and some information from his adoption.