Romney as candidate - yes, that absolutely guarantees Obammny wins. No true Conservative is going to vote for either one. You can act like a battered wife and continue to get slapped around by the GOPe, or you can fight FOR Conservatism. It is becoming ever more apparent that the GOP is no longer a natural home for Conservatives, so good luck to all the Olympia Snowe wannabees and their 21st Century Whig Party.
Are you old enough to remember 1992? It may be a cliche but the advice to divide and conquer still applies.
Rather than wishful dreaming look at the numbers. Probably forty percent of the electorate are broken glass Democrats. Giving you the best case scenario let us assume that twenty percent of the electorate are dyed-in-the-wool Republicans. Adding together the highly committed voters of the two major parties brings the committed voters to 60. So the third party ticket would have all of the uncommitted electorate just to tie Obama which would be almost completely impossible.
In addition to the statistics, the third party would have qualify in all the states and would have raise huge sums of money in a short period of time. Furthermore, one cannot ignore the hostility of the MSM to Palin. The MSM will absolutely do its utmost to destroy Palin. Conversely, the MSM will support Obama and MSM support has been estimated to provide about a five percent edge.