Probably most would (TR's voters were basically Progressive Republicans) but either man would need well over 90% of the combined Taft/TR vote, or else crucial states like NY and Ohio, where the combined vote exceeded the Wilson vote by only seven or eight percentage points, would start to fall away. Combined with the South and Border states, that would give Wilson a majority.
I actually don't think it's safe to say that most would. By this point, Pinchot/Ballinger and the House revolt have already occurred, and the progressives are in full rebellion against Taft and the regular Republicans. Without TR, many, perhaps most, would have found some other outlet, whether it's the Dem nominee, La Follette as some have suggested or another third-party nominee (maybe even Debs), or sat on their hands.