3 man mechanics question

[shipwreck]

I have been reviewing 3 man mechanics for our State Tourney. Here is my question. I have been told if a base umpire goes out that you revert to a two man rotation, and I understand that. Runner on second base. Base ump goes out on a ball in the air. The 3 man says if one base ump goes out that the plate umpire will take the runner on second, to third and home. But in a straight 2 man, the base umpire would take the runner on second to third. Is this all correct and how many other situations are there that you don't in fact revert to a 2 man when a base umpire goes out on a fly in a 3 man? Dave