This hypothetical is so far from the 2000 election as to be unrecognisable. If I'd written "If Nader takes enough votes from Bush..." it would be about as realistic.

In any case, if Gore preferences flow to Bush over Nader, that's because those voters are expressing their preference for Bush over Nader. That's not spoiling: it's literally the entire point of providing a full ranking, is so that nobody's vote is ever discarded and so that any winning candidate must have accumulated an absolute majority.