[Sopater]

...why does the rule “revert” if the Democrats lose control of the Senate?

I have not been able to find this "clause".

[Leaning Right]

...why does the rule “revert” if the Democrats lose control of the Senate?

I have not been able to find this "clause".

I'm just guessing here, but perhaps a procedural change such as this only applies to the current Senate, and automatically expires when a new Senate is seated (in 2015).