I agree with you, this could happen.
But couldn't the slate of electors for a given state, under this method, also be rejected and the race thrown into the house of representatives?
Basically, what you are saying is that the Dems could put up a candidate that wins the race, Zell Miller for example. Then the party takes him out by some nefarious means, and tells the electors to vote for someone else who could never have actually won the race on their own (Hillary).
There has to be some check and balance to stop this from happening.
When the electoral votes are counted before Congress on January 6, members of Congress can challenge electoral votes and vote to throw them out. In a tight race, this would certainly lead to the election being thrown into the House.
But if a party picked a new ticket due to death or the resignation of a candidate due to scandal or disease, there would be no grounds for challenge. The key to challenge is fraud in a given state. You have to go back to 1876 for that one.
There has to be some check and balance to stop this from happening.
That is one of the many problems with the Electoral College. People on both the Left and Right have pointed out that the Electoral College is an accident waiting to happen. (This isn't the thread to go into possible ways of remedying problems with the EC.)