What happens if President elect Biden dies before being sworn in?

In 2008 when Nader won with Gonzalez and Nader peacefuly passed on in his sleep the night of the election, the Country became rent and repeated a segment of Time.  Nader did not win the second Time; Obama, an unheard of, stole the election.  If our government has done its job, new safeguards are in place.

Now or after the electoral vote?  After all, that is the one that actually votes in the president and the VP. Once that happens, the VP, the chain will be in place and we will go from there.

That would be a Constitutional crisis.

Kamala Harris becomes president on January 20th based on current law.

Cameltoe becomes President.

The presidency would go to whoever the electoral college chose to replace him, I am sure that would be Kamela Harris though I am sure some though would make an argument for Donald Trump to get it since he is the 2nd place candidate in the election. 

Kamala Harris would assume the presidency and Nancy Pelosi would assume the position of vice president.

The presidency would go to whoever the electoral college chose to replace him, most likely Harris.