it is hard to say what voters would really do given a certain situation.
It is already hard enough to find a rational argument for voters picking McCain over Ron Paul (especially if 70% of American's want out of the war and they can see our economic meltdown that Ron Paul has been predicting for years happening in front of their face).
Our traditional reason we most often come back to is: "people just didn't know about Ron Paul and were either misinformed, too lazy to educate themselves, too stubborn to listen, or were brainwashed by the media."
There are just so many dynamics that go into it. Am I the only one who feels that McCain has all of these "votes" yet few actual supporters? Everywhere you look people hate McCain. Maybe it is Huck and Romney supporters that feel tricked since they often voted for their man because they DIDN'T want to vote for McCain, only to then find their candidate turn around and endorse the guy like good little Republican puppets.
Is it possible that 20 - 30% of Republicans would vote for someone other than McCain if given a reasonable candidate to rally behind? Yes, it's
possible, but hard to really predict. It is also important to remember that there are MANY MANY people in the U.S. that do not participate in the primaries. It is hard to say what they will do in a General election.
Ron Paul doesn't want to run 3rd party or Independent for several good reasons.
- He's tried this before and he knows how difficult it is
- There is often a large challenge to just get on the ballot
- He may not be invited to a single debate. This will be a slugfest against McCain and Clinton/Obama.
- His long term goal is to take over and change the Republican party and he may severely damage his standing in the party if he runs 3rd party or Independent
- Under the same scenario that might make a 3rd party or Independent run viable for Ron Paul... would Bloomberg enter the race?
But there are several good reasons why he SHOULD run too.
- His Republican primary campaign has already given him some name recognition so he may already be in the minds of many people rather than trying to build that brand from scratch. There are many people that started researching Ron Paul and have joined the cause AFTER their primaries were over. Many others (including friends of mine in California) couldn't vote for Ron Paul because they were registered Independent but they would vote for him in a General election.
- He has proven that he can raise money and he may be able to raise 2-3 times what he did in the primaries
- There are a lot of conservative Republicans that DO NOT want to vote for McCain but don't really see another choice. Would they vote for Ron Paul? Possibly.
- The Democratic party has been polarized. We don't know how this is going to play out though. Would Obama accept a VP slot? Would one of them endorse the other? Would the loser run independent themselves? Given the right scenario, it is possible that many Obama supporters (including a lot of independent voters) could vote for Ron Paul as a second option. But it is hard to say.
- Though Ron Paul's long term goal is to change the Republican party from within, his "standing" is ALREADY damaged. His own party doesn't like him OR his supporters. WE can still take over the party and work towards that end goal but HE doesn't need to. Realistically, how much longer will his political career be anyway? 5 years? 10 years? Is he going to run for President or Congress at the age of 86? At some point (relatively soon) another person will have to emerge to lead this Movement and THAT person can continue to work within the Republican party, so what can it hurt for Ron Paul to take a chance now?
- Ron Paul announcing an independent or third party bid would turn this entire political landscape upside down, at time when the media and other campaigns are starting to make some sense of things. RP would throw a wrench in all of their planning. It would re-energize the base and he might raise another 30 million in 3-4 weeks. Ron Paul has the ability to pull independents away from the Democrats and conservatives away from the Republicans.
I've often thought that it would be an awesome political move to FORCE the Republican party and John McCain to keep Ron Paul from running. PUBLICLY ask them to embrace the Conservative Right of the party and bring the party back to its roots or he will be left with no CHOICE but to run against McCain and give Conservatives a choice. 
Put the ball in their court and FORCE them to make a decision. They will either support the Ron Paul (conservative) platform or publicly alienate half of their party and virtually guarantee a loss in the General election.
Knowing the GOP, they'll probably say something to the affect of "F*CK YOU, we wont be blackmailed". But that move might be all Ron Paul would have needed to galvanize the base around him because it shows all Conservative Republicans that their party really HAS broken away and no longer supports their views.
But though this is fun to talk about, these are all hypothetical situations. We have to listen to Ron Paul. It isn't like he hasn't thought about it. He's even had third party offers and has turned them down. We can't FORCE him to run (as much as many people would like to).