Christie might not have anything to say about this if the courts get involved.
Remember Robert "The Torch" Torricelli? His scandal was about to take him down just before the election, and the Rat-controlled NJ supreme court forced a replacement candidate (Lautenberg) to be put on the ballot, after the date at which such a replacement would have been legal. The argument was that the people deserved a choice, and with one candidate unelectable, they woudn't have that choice.
With Menendez, the argument will be that the people picked a Rat, so they should get another Rat.
Christie will cave. That's a given.
For those who may not know, if Menendez leaves this year or next year there will be 2 US Senate races in NJ in November 2014.