Giuliani, IMHO, could win huge. He'll definitely take NY, and would force Hillary to campaign in California. The Rats have no chance if they lose NY and California. Hillary will never be competitive in the south, except for maybe Louisiana.
See my remarks above, though, about a liberal Republican's potential to split the party.
Too, what you have to watch out for in the general, is not the GOP'ers who would stay home, but as 2006 pointed out, the MOR indy swing voters who, confronted with a choice between a Republican who sounds more liberal than a Republican and a Democrat who is identifiable with the liberal party, tend to drift away from their "Reagan Democrat" voting pattern and just go with the 'Rats.
That's what Rahm Emanuel's strategy was all about last fall with the "conservative" Democrats he ran. (Interesting how he wound up being the kingmaker in all those local Democratic nominating races, yes? -- nobody's screaming in the MSM about "King Rahm", though, they way they do about Rove, are they? And that raises another question: If Rahm was doing all that, and Rahm is an old Clintonista........then was he working for Bubba the whole time????).
The entire point is that when the contest's between a 'Rat playing middle-of-the-road (lying her ass off, IOW) and a Republican who sounds MOR, the Reagan Democrats vote 'Rat.
Can I make this point loudly enough? Liberal Republicans are a Bad Idea.