Obviously it will be a split. I think Hunter, Thompson and Huckabee will all get hefty shares. McCain might get some, but probably less than you think. McCain would get a lot if Romney were his old self. The new Romney appeals to different voters. Now, if Thompson drops out McCain should get his votes. Only there is an odd phenomenon with that. Thompson voters hate McCain even though the two candidates are very similar. So I don't see McCain pulling in any votes from other Republican candidates. He might benefit from the dropout of some Dem candidates.
I don’t see Thompson dropping out just yet. It will take more than just a loss in Iowa and New Hampshire. A lot will likely depend on South Carolina.
I think Ron Paul voters would like McCain except that he is too much of a hawk for their taste.