I read this rule totally differently.
As far as I can tell:
Your command section can only function if it has a unit leader.
If you have at least one command section with a unit leader, then you're good to go, but can only use those sections with a unit leader to give orders, etc.
If you have no command sections with a unit leader, then you will have to find a different section that has a unit leader to be your command section, and pay an order (unless the unit leader is a hero) to make that section the command section for that turn, and you only have 6" order radius.
BUT, since you promot miniatures to unit leaders in the unit phase, if during that time your command section gains a unit leader, in the next command phase, everything is back to status quo, and you're good to go with your 12" radius and using your command section to give orders, since you have a command section with a unit leader.
This to me makes the most sense with the rules as written. This idea of "original unit leader" vs "current unit leader" just isn't anywhere in the rules as far as I can tell, and the example people are quoting from the rules only happens if "each" (i.e. every) command section unit leader is lost, so saying that if one of your multiple command sections loses its original leader, it's down to 6" radius forever, doesn't make sense, as the rules being quoted here wouldn't even be triggered in that situation.